108 GERMICIDAL PROPERTIES OF BLOOD SERUM. 



tons, and we know that peptons are especially favorable to bacterial 

 growth. 



2. The germicidal substance must belong to the proteids. Other- 

 wise it would be difficult to explain the fact that a temperature of 

 55° renders blood serum inactive. 



3. The only proteid likely to be present in blood serum and which 

 is not destroyed by peptic digestion is nuclein. Having reached 

 these conclusions, the following questions naturally presented them- 

 selves: 



1. Is there a nuclein in blood serum? 2. Has this nuclein, if 

 there be one, germicidal properties ? 



The first of these questions was answered in the following manner : 

 An active blood serum was treated with ten times its volume of a 

 mixture of equal parts of absolute alcohol and ether. This produced 

 a voluminous precipitate which, after repeated washings with alcohol 

 and ether, was submitted to the action of pepsin-hydrochloric acid 

 in the incubator at 38°. Digestion was continued until the super- 

 natant fluid failed to respond to the biuret test for peptons. Each 

 time this test was made the fluid was decanted from the undigested 

 part and replaced by an equal volume of fresh digestive fluid. In 

 all cases, digestion was prompt and proceeded to a certain point, 

 when it ceased altogether. The undigested proteid was small in 

 amount and grayish in color. This was collected on a small steril- 

 ized filter, and washed first with a 0.2 per cent, solution of hydro- 

 chloric acid, and then with alcohol. After the washing with alcohol, 

 the filter was allowed to stand exposed to the air for half an hour or 

 longer in order that all of the alcohol might pass through or evap- 

 orate. The precipitate was then dissolved in a sterilized solution of 

 potassic hydrate. The strength of this alkaline solution usually em- 

 ployed was 0.12 per cent, and the solution contained in addition to 

 the alkali 0.6 per cent, of sodium chlorid. In some instances a 

 solution containing 1.2 grams of potassic hydrate, six grams of 

 sodium chlorid, and one gram each of sodium bicarbonate and diso- 

 dium hydrogen phosphate to one liter of water, was employed as a 

 solvent. The solution was filtered through a Chamberland tube and 

 received in a sterilized flask. The solution thus obtained was per- 

 fectly clear, colorless, and did not respond to the biuret test. The 

 addition of strong nitric acid produced a cloudiness, which dissolved 

 on the further addition of the acid. This acid solution did not be- 

 come yellow on being heated, but did so after the addition of am- 

 monia. It is true that there was no ultimate analysis made of this 

 substance, but the above experiments demonstrate the fact that blood 

 serum contains a proteid which resists peptic digestion, does not re- 

 spond to the biuret and xanthoproteic tests, and which, as we shall 

 see later, has marked germicidal properties. Is this substance serum 

 albumin or is it a nuclein ? Moreover, the presence of nucleinic acid 



