<informationTable xmlns="http://www.sec.gov/edgar/document/thirteenf/informationtable">		<infoTable>
			<nameOfIssuer>CODEXIS INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>192005106</cusip>
			<value>3682</value>
			<shrsOrPrnAmt>
				<sshPrnamt>1805000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>1805000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>CRESTWOOD MIDSTREAM PARTNERS</nameOfIssuer>
			<titleOfClass>UNIT LTD PARTNER</titleOfClass>
			<cusip>226378107</cusip>
			<value>6415</value>
			<shrsOrPrnAmt>
				<sshPrnamt>284620</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>284620</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ENERGY TRANSFER EQUITY L P</nameOfIssuer>
			<titleOfClass>COM UT LTD PTN</titleOfClass>
			<cusip>29273V100</cusip>
			<value>17587</value>
			<shrsOrPrnAmt>
				<sshPrnamt>376200</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>376200</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ENTERPRISE PRODS PARTNERS L</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>293792107</cusip>
			<value>31040</value>
			<shrsOrPrnAmt>
				<sshPrnamt>447517</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>447517</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>FIBROCELL SCIENCE INC</nameOfIssuer>
			<titleOfClass>COM NEW</titleOfClass>
			<cusip>315721209</cusip>
			<value>48218</value>
			<shrsOrPrnAmt>
				<sshPrnamt>9219512</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>9219512</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>FIBROCELL SCIENCE INC</nameOfIssuer>
			<titleOfClass>COM NEW</titleOfClass>
			<cusip>315721209</cusip>
			<value>31510</value>
			<shrsOrPrnAmt>
				<sshPrnamt>6024915</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>DFND</investmentDiscretion>
			<votingAuthority>
				<Sole>6024915</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>GENESIS ENERGY L P</nameOfIssuer>
			<titleOfClass>UNIT LTD PARTN</titleOfClass>
			<cusip>371927104</cusip>
			<value>11761</value>
			<shrsOrPrnAmt>
				<sshPrnamt>217000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>217000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>HALOZYME THERAPEUTICS INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>40637H109</cusip>
			<value>251547</value>
			<shrsOrPrnAmt>
				<sshPrnamt>19791286</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>19791286</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>INTREXON CORP</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>46122T102</cusip>
			<value>1641528</value>
			<shrsOrPrnAmt>
				<sshPrnamt>62439273</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>62439273</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>KINDER MORGAN ENERGY PARTNER</nameOfIssuer>
			<titleOfClass>UT LTD PARTNER</titleOfClass>
			<cusip>494550106</cusip>
			<value>23523</value>
			<shrsOrPrnAmt>
				<sshPrnamt>318098</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>318098</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>MARTIN MIDSTREAM PRTNRS L P</nameOfIssuer>
			<titleOfClass>UNIT L P INT</titleOfClass>
			<cusip>573331105</cusip>
			<value>6104</value>
			<shrsOrPrnAmt>
				<sshPrnamt>141800</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>141800</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>NUSTAR ENERGY LP</nameOfIssuer>
			<titleOfClass>UNIT COM</titleOfClass>
			<cusip>67058H102</cusip>
			<value>6402</value>
			<shrsOrPrnAmt>
				<sshPrnamt>116500</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>116500</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ORAGENICS INC</nameOfIssuer>
			<titleOfClass>COM NEW</titleOfClass>
			<cusip>684023203</cusip>
			<value>2872</value>
			<shrsOrPrnAmt>
				<sshPrnamt>1000555</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>1000555</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ORAGENICS INC</nameOfIssuer>
			<titleOfClass>COM NEW</titleOfClass>
			<cusip>684023203</cusip>
			<value>25367</value>
			<shrsOrPrnAmt>
				<sshPrnamt>8838666</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>DFND</investmentDiscretion>
			<votingAuthority>
				<Sole>8838666</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>OVASCIENCE INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>69014Q101</cusip>
			<value>894</value>
			<shrsOrPrnAmt>
				<sshPrnamt>100000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>100000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>OVASCIENCE INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>69014Q101</cusip>
			<value>2443</value>
			<shrsOrPrnAmt>
				<sshPrnamt>273224</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>DFND</investmentDiscretion>
			<votingAuthority>
				<Sole>273224</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>PLAINS ALL AMERN PIPELINE L</nameOfIssuer>
			<titleOfClass>UNIT LTD PARTN</titleOfClass>
			<cusip>726503105</cusip>
			<value>22048</value>
			<shrsOrPrnAmt>
				<sshPrnamt>400000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>400000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>REGENCY ENERGY PARTNERS  L P</nameOfIssuer>
			<titleOfClass>COM UNITS L P</titleOfClass>
			<cusip>75885Y107</cusip>
			<value>4512</value>
			<shrsOrPrnAmt>
				<sshPrnamt>165750</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>165750</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>SYNTHETIC BIOLOGICS INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>87164U102</cusip>
			<value>22297</value>
			<shrsOrPrnAmt>
				<sshPrnamt>8675768</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>DFND</investmentDiscretion>
			<votingAuthority>
				<Sole>8675768</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>SYNTHETIC BIOLOGICS INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>87164U102</cusip>
			<value>9316</value>
			<shrsOrPrnAmt>
				<sshPrnamt>3625000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>3625000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>TC PIPELINES LP</nameOfIssuer>
			<titleOfClass>UT COM LTD PRT</titleOfClass>
			<cusip>87233Q108</cusip>
			<value>4649</value>
			<shrsOrPrnAmt>
				<sshPrnamt>97000</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>97000</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ZIOPHARM ONCOLOGY INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>98973P101</cusip>
			<value>6528</value>
			<shrsOrPrnAmt>
				<sshPrnamt>1425403</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>SOLE</investmentDiscretion>
			<votingAuthority>
				<Sole>1425403</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
		<infoTable>
			<nameOfIssuer>ZIOPHARM ONCOLOGY INC</nameOfIssuer>
			<titleOfClass>COM</titleOfClass>
			<cusip>98973P101</cusip>
			<value>75068</value>
			<shrsOrPrnAmt>
				<sshPrnamt>16390305</sshPrnamt>
				<sshPrnamtType>SH</sshPrnamtType>
			</shrsOrPrnAmt>
			<investmentDiscretion>DFND</investmentDiscretion>
			<votingAuthority>
				<Sole>16390305</Sole>
				<Shared>0</Shared>
				<None>0</None>
			</votingAuthority>
		</infoTable>
</informationTable>
