176 THE BLOOD. 



1. Filtration of the Blood of the Frog. Of three test 

 tubes (Fig. 190), each capable of holding about two drachms 

 of liquid, No. 1 is filled to about one-fifth of its depth with a 

 solution of sulphate of soda obtained by mixing one volume 

 of saturated solution with one of distilled water ; No. 2 con- 

 tains about half a drachm of half per cent, solution of sugar ; 

 No. 3, half per cent, solution of chloride of sodium. Several 

 frogs are then selected, in each of which the pericardium is 

 exposed and divided as directed in 46, and a snip made in 

 the ventricle with fine scissors, the integument having been 

 dried with filtering paper before making the first incision. 

 The blood is allowed to flow into No. 1 until four times as 

 much blood has been added to the quantity of solution as the 

 tube previously contained. To each of the liquids in No. 2 

 and in No. 3 an equal volume of blood is added. Each of the 

 liquids is gently agitated and then thrown on a filter made of 

 strong close-fibred paper prepared for its reception, and corre- 

 spondingly numbered. In each instance we obtain a clear and 

 colorless filtrate, the whole of the colored part of the blood, 

 i. e., the corpuscles, being collected on the filter. The three 

 filtrates have, however, different characters. From filter No. 

 1 is obtained a liquid which remains fluid at ordinary temper- 

 atures, i. e., provided that the room is moderately cool. From 

 filter No. 2 we have a liquid which coagulates immediate!}'. 

 From No. 3 a liquid which coagulates after a time : its coagu- 

 lation will be much accelerated if it is placed in a bath, at a 

 temperature approaching that of the body. 



In the sulphate of soda filtrate the appearance of a clot is 

 postponed indefinitely. It is, however, not the less certain 

 that it really contains the immediate principles of which fibrin, 

 the material of the gelatinous mass seen in the other tubes, is 

 formed. This may be demonstrated by diluting the liquid 

 with distilled water. If the original solution had been satu- 

 rated, water might have been added gradually for some time 

 without producing any apparent change. In the present in- 

 stance, the solution employed contains one part of saturated 

 solution to one of distilled water. If water is added to the 

 mixture in the proportion of one-fifth of its volume, it is suffi- 

 cient to render it coagulable, whereas six or seven volumes 

 would have been required if the solution had been concen- 

 trated. As, therefore, saturated solution of sulphate of soda 

 contains fifty per cent, of the crystalline salt, this last must, 

 in order to the prevention of coagulation at ordinary tempera- 

 ture, be present in a proportion of not much less than five per 

 cent. 



In these experiments it has been shown (1) that the colored 

 blood corpuscles of the frog are so large that they do not pass 

 through close filtering papers ; (2) that in the filtrate, even 



