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Scientific Proceedings (68). 



it became evident that the histologic method was so delicate an 

 indicator that unmistakable evidence of the action of normal 

 serum on animal tissue was readily demonstrable. The activity 

 of the serum varies greatly with the species of animal from which 

 the serum is derived. Of those investigated the serum of the cat 

 is apparently one of the most powerful and it is with the normal 

 serum of this animal that the present investigation was chiefly 

 concerned. 



The serum was obtained from the jugular vein and immediately 

 centrifuged ; in this manner best avoiding the mechanical hemolysis 

 which is likely to occur. At first, in addition to the boiled tissue, 

 we attempted to use formalin and acetone fixed sections but 

 found that these fixatives almost entirely inhibited the action 

 of the serum. 



In our more recent work we have used fresh and boiled tissue 

 almost exclusively. The use of fresh tissue theoretically did not 

 promise much, as, on the authority of Abderhalden, it has long 

 been assumed that only in the boiled state do the tissue proteins 

 undergo digestion. Moreover, the work of Longcope and others 

 has shown that serum has a preservative action on tissue. This 

 author, however, calls attention to the fact that in the most super- 

 ficial layers of the block of tissue immersed in serum, the nuclei 

 do not stain, and it is apparently these changes that we are con- 

 cerned with in our present investigation. In the use of fresh 

 tissue, the factor of autolysis is involved. But as Launoy has 

 shown with the guinea-pig liver, and as we have been able to 

 confirm, marked histologic evidence of autolysis does not appear 

 within the first 24 hours, if the temperature is kept below 37.5 

 degrees C. Our sections were incubated from 18-21 hours, and 

 in only a few instances did our controls show marked autolytic 

 changes, when needless to say that particular experiment was 

 rejected. 



When boiled tissue was used as substrate, small blocks about 

 2 cm. in thickness were cut, washed in water, then thrown in 

 physiological salt solution and boiled for fifteen minutes. Frozen 

 sections, 10 microns in thickness, were made of the fresh and 

 boiled organs. 



The activity of the serum was determined by a series of dilu- 

 tions, I, 1/10, 1/20, etc., in physiological salt solution. 



