360 BACTERIA. 



dimethyl piperidine, and so on throughout the whole group. In fact, where 

 there are so many bonds to be acted upon the number 

 of organic compounds is almost endless, and it can 

 be readily seen how substances varying much in 

 chemical composition can still be arranged in groups 

 under a common head ; the members of each "series 

 having very much in common not only as regards 

 CH 2 their chemical character, but, as has recently been 

 pointed out, as regards their physiological action. As 

 a considerable number of the benzol series have been 

 manufactured by the chemist, it comes quite within 

 the range of possibility that a number of the ptomaines 

 r (especially those of the pyridine series) may also be 



CH 2 built up synthetically. 



The most important of the methods used for the sepa- 

 ration of the ptomaines is that used by Brieger, who is 

 perhaps the greatest authority on this subject. He 

 goes to work with the salts of the heavy metals, and 

 with picric acid. When he wishes to separate an 

 alkaloid from any putrefying mass, this mass is first 

 boiled with water, and then filtered ; the filtrate is then 

 treated with sub-acetate of lead ; from this the lead is precipitated by 

 sulphuretted hydrogen which is passed through the filtrate, and the fluid is 

 again filtered to keep back the lead sulphide. This second filtrate is 

 evaporated to about one-third of its original bulk, and is mixed with amyl- 

 alcohol, it is then thoroughly washed with water, and again reduced in bulk 

 by evaporation, and sulphuric acid and ether are added ; the ether is 

 evaporated, after which the remaining liquid is concentrated by careful 

 evaporation to one-third of, or one-fourth of, its bulk ; the evaporation 

 driving off most of the volatile fatty acids present, after which the fluid 

 neutralized by the addition of baryta, is again filtered, carbonic acid gas 

 is passed through it, by which baryta carbonate is thrown down which 

 is separated by filtration. After careful heating over a water bath, the 

 fluid is cooled, and bichloride of mercury is added, when a somewhat 

 dense precipitate is formed. This precipitate is carefully washed and 

 decomposed by sulphuretted hydrogen, when sulphide of mercury is 

 thrown down; the fluid is again filtered and the filtrate is evaporated 

 to obtain as great concentration as possible. From the liquid so ob- 

 tained all inorganic substances crystallize out first ; these are removed, 

 and then in the fluid that remains "organic" acicular crystals are 

 thrown down. These may be dissolved in water, but they are insoluble in 

 absolute alcohol, ether, benzine, or chloroform. It is found that the sub- 

 stances so given, the ptomaines, may be precipitated by the salts (especially 

 the chlorides) of the heavy metals. These precipitates or crystals 

 differ, however, very considerably as to their solubility ; hydrochloride of 

 putrescine obtained by the above method separates out in acicular crystals, 

 and on the addition of chloride of gold gives very insoluble crystals of an 

 octahedral form, whilst on the addition of chloride of platinum, octahedral 

 crystals which are much more soluble, are also formed. Phospho- 

 molybdic and phospho-wolframic acid added to this substance give respec- 

 tively a yellow and a white crystalline precipitate. Iodide of mercury 

 dissolved in iodide of potassium also gives rise to the formation of prisms ; 



