PEPTONE. 39 



of Kiihne 1 in Heidelberg, and of Chittenden 2 who now 

 works independently of his old master in the laboratory of 

 Yale University. 



In his first paper Kiihne states in general terms that 

 a solution containing a mixture of proteoses and peptone 

 gives a precipitate of proteoses when saturated with 

 ammonium sulphate, the peptone remaining in solution. 

 After filtration, the filtrate if set aside will subsequently give 

 a further precipitate if more salt is added. This has been 

 explained by supposing that the saturation was in the first 

 case incomplete, or that the peptone is partially changed 

 back into proteose. He proceeds to show that the former is 

 the more probable explanation. There are many precau- 

 tions necessary in order to precipitate the last traces of 

 proteose. It is necessary in the first instance to use large 

 volumes of the saturated solution in addition to merely 

 adding crystals of the salt to the proteid mixture. Further, 

 it is found that whereas the greater part of the proteose is 

 precipitated by the salt if the reaction of the mixture is made 

 acid, the residue, which is difficult of precipitation, comes 

 down more readily if the reaction is made alkaline. It is 

 further necessary, after the solution of peptone is obtained, 

 to remove the salt employed ; this may be accomplished by 

 the use of barium carbonate after concentration. If pan- 

 creatic juice is used for the preparation of peptone, care 

 must be taken to remove leucine and tyrosine also. In 

 drying, concentrating, etc., especially if sulphuric acid is 

 used, a brownish product is formed ; this is minimised by 

 care in the manipulations. This substance is precipitated 

 by ammonium sulphate ; it is not however albumose ; it 

 gives no biuret reaction. Further, if a precipitate forms on 

 dialysis, it is not necessarily of proteid nature ; if hard 

 water is used it may be calcium sulphate. 



Pekelharing does not seem to have recognised the 

 necessity of these and other precautions and details ; and, 

 moreover, the differences between peptone and proteose 

 are very striking. This aspect of the subject is considered 



1 Zeit. Biol., xxix., pp. i and 308. a Journ. of Physiol, xvii., p. 48. 



