CHAPTER XXVI. 309 



and the zoologist especially is advised to get the help of an expert 

 on enzymes before attempting to interpret any experiments he may 

 have made with such intra-cellular enzymes. Because a certain 

 protease will not dissolve away a given cell granule, while a 

 " nuclease ' may do so, does not by itself provide good evidence 

 for the conclusion that the granule in question is " chromatin," or 

 derived from the chromosomes. 



VAN HERWERDEN (A rch. f. Zellf., x, 1913) for instance, using the 

 extract of spleen containing " nuclease," finds that the granules identi- 

 fied as " chromatin " emission by Schaxel are dissolved away. In all 

 probability, however, such granules are phospholipin and not chroma- 

 tinic, and were dissolved away by some lipolytic enzyme in. the solution 

 used by Van Herwerden. 



Successful experimentation on this side of cytology calls for two 

 desiderata : Firstly, an intimate knowledge of the nature of the 

 enzyme solution to be used, and of what effects the latter has on 

 various definitely identified categories of cell substances ; second, 

 a thorough study of the origin and microchemical reactions of the 

 body to be treated by the enzyme solution. See VERNON, Infra- 

 Cellular Enzymes, London, John Murray, 1908 ; BAYLISS, The 

 Nature of Enzyme Action, Longmans, Green & Co., 1920 ; EULER, 

 General Chemistry of the Enzymes, Pope's Translation ; BAYLISS, 

 General Principles of Physiology, 1919. 



665. Method of Using Enzyme Solutions. These should be used on 

 fresh cells. It is best to begin by identifying cell or nuclear bodies or 

 granules in properly fixed and stained preparations ; after this one 

 should familiarise oneself with the appearance of such granules or 

 bodies in the fresh cells, with and without intra- vital staining. 



The enzyme or digesting fluids may be added to fresh cells, a coverslip 

 provided, and the preparation observed at intervals under a high power. 



Another method is to immerse pieces of fresh tissue in the digestive 

 fluid for suitable times, and then fix the tissue in some mixture by 

 previous trials indicated for the purpose ; controls should be made by 

 soaking other pieces of tissue for a similar time in some of the same 

 solution inactivated by heat, or without the added enzyme. 



As indicated above, such tests are of doubtful value as regards the 

 identification of " chromatin " ; the solutions used should be tried 

 carefully on cells whose cytology is thoroughly known by the observer. 

 The use of proprietary " pepsins " and such-like solutions whose origin 

 and method of manufacture are unknown to the worker, is not likely to 

 lead to the best results. See also C. BECKWITH, Jour. Morpli., xxv, 

 1914, and JORGENSEN, Arch. f. Zellf., x, 1913, and 645. 



666. Chromophility. Some workers indiscriminately call all 

 basophil chromatic material chromatinic, which is unjustifiable : 



