Mechanism of immunity against micro-organisms 197 



of sulphuric acid). Once the serum becomes distinctly acid the 

 bactericidal power disappears at once. 



Our knowledge of the cytases, as a whole, leads us to approximate 

 these diastases to the group of trypsins, papain, amoebodiastase and 

 actinodiastase. The cytases are elaborated by the phagocytes, but 

 are not secreted into the plasmas and they remain inside the cells so 

 long as these cells remain uninjured. 



In this respect the cytases must be placed in the group of the 

 " Endo-enzymes," according to the nomenclature of Hahn and Geret 1 . 

 These observers have carefully studied the proteolytic diastase of the 

 yeast of beer which likewise acts inside the cells without ever being 

 excreted. This diastase, to which they give the name of "yeast endo- 

 trypsin" (Hefeendotrypsin), presents in general an undeniable rela- 

 tionship with the phagocytic cytases, from which it is distinguished [208] 

 however by a greater sensitiveness to alkalis. Kutscher 2 in his 

 researches on autodigestion in yeast has established analogous facts. 



The cytases and endotrypsin are consequently endo-enzymes, as 

 are also amoebodiastase, actinodiastase, plasmase (fibrin ferment) 

 and the zymase of E. Buchner. All remain confined within the cells 

 which have manufactured them and are not secreted or excreted, as 

 are the sucrase and invertin produced by yeasts or Mucediuae. 



Our present knowledge on the cytases is as yet far from perfect, 

 which is not astonishing, seeing how recently the question has been 

 brought forward. The cytases found in the serum of the same animal 

 are the same, for we have seen that the macrocytase which dissolves 

 red blood corpuscles is the same which digests spermatozoa ; whilst 

 the same microcytase digests bacilli, spirilla, and cocci. But in the 

 serums of different species, the cytases differ. Thus the cytases of 

 the dog are not the same as are those found in the serums of the 

 rabbit or horse. Whilst the majority of the cytases are very sensitive 

 to heat and are destroyed at a temperature of 55 56 C., some, 

 e.g. the microcytase of rat's serum, resist this temperature and are 

 only destroyed at 65 C., presenting, consequently, an example of 

 cytase stable to heat similar to that discovered by Ehrlich and 

 Morgenroth. 



It is as yet very difficult to establish whether, besides the cytases, 

 there exist other endo-enzymes within phagocytes, that is to say, 

 soluble ferments which do not pass into the serums on the destruction 



1 Ztschr. f. iol., Miinchen u. Berlin, 1900, Bd. XL, S. 117. 



2 Sitzungsb. d. naturforsch. Gesellsch. zu Marburg, 1900. 



