21. Experimental systems include mouse models, cultured neurons, large model synapses, isolated synaptic preparations and cell free systems . 22. Because Linux is a free system , whose code can be manipulated by anybody, it also breeds variation. 23. On one end there are those who oppose every restriction on the most free system of exchanges. 24. In 2008 he started to smoke marijuana with a carbon-free system to avoid the effects of smoke. 25. Such algorithms preserve the source-free systems . 26. For a truly pollution-free system , environmentalists argue, the hydrogen must come from a source that does not pollute. 27. A 24 / 7 toll-free system will be introduced, 138 for the helpline and 182 for security issues. 28. Germany's tuition-free system costs a total of about 50 billion marks ( dlrs 28.5 billion ) a year. 29. Among metal-free systems , dioxiranes are the best oxidants for the conversion of C-H bonds to alcohols or carbonyls. 30. However, he qualified his belief in civil liberties to exclude what he considered threats to a free system .
