of the Fishery Board for Scotland. 



173 



The similarity of the chemical and microscopical properties of this body 

 to fibrin naturally leads one to infer that it may be formed in a similar 

 manner, namely, by the solidification of a previously-soluble proteid or 

 fibrinogen, and this supposition turns out to be a true one. This is 

 brought out by the consideration of the following seven points, which 

 show the resemblance of the process of coagulation to that observed in 

 vertebrate blood : — 



1. It does not take place in the living vessels. .* 



2. It takes place after the blood is shed. 



3. It can be prevented by the admixture with the blood of certain 

 large proportions of neutral salts. This is in contradiction to what 

 previous investigators on the subject of crustacean blood have said 

 (Fredericq^ Extrait des bidletins de VAcad. Roy ale de Belgique^ tome 

 xlvii., No. 4. 1879. Kruhenher-g, Vergl. Phys. Studien, 2te Heihe, 

 Ite Ahth., s. 49. Heidelberg, 1882). They did not apparently use a 

 sufficiently large amount of such salts. It is necessary to have at least 

 four times as much saturated solution of magnesium sulphate, or ten 

 times as much saturated solution of sodium chloride, as of blood. 

 Sodium sulphate does not prevent the coagulation : this is difi^erent to 

 what obtains among vertebrata. Subsequent dilution of this salted 

 blood with water brings about coagulation. 



4. The formation of the fibrin is due to the solidification of a proteid 

 body or fibrinogen, which exists in solution in the blood planera. This 

 can be precipitated by saturating with magnesium sulphate or sodium 

 chloride, washed and redissolved by water. The addition of fibrin 

 ferments, prepared either from crustacean or from mammalian blood, to 

 this solution brings about the formation of fibrin. 



5. This conversion of fibrinogen into fibrin is brought about, as indicated 

 in the last paragraph, by a ferment action. 



6. The source of this ferment is the amoeboid corpuscles of the blood. 

 The ferment can be prepared from the blood by Schmidt's method ; that 

 is, precipitation by alcohol and subsequent extraction of the dried 

 alcoholic precipitate by water. This ferment is identical with that of 

 mammalian blood, and brings about coagulation in hydrocele, pericardial, 

 and similar fluids, just as the ferment prepared from mammalian blood 

 does. 



7. Coagulation can be prevented by cold. 



III. — The Peoteids of the Plasma and Serum. 



The proteids of the blood plasma are two in number, namely — haemo- 

 cyanin and fibrinogen. The blood serum contains only the former of 

 these, hsemocyanin. 



1. Hcemocyanin. — This is an interesting body, occurring pretty widely, 

 distributed in various classes of the invertebrata (Cephalopoda, Gastro- 

 poda, Crustacea, Arachuida). The properties that have been hitherto 

 ascribed to it are as follows : — 



(a.) It gives the ordinary proteid reactions. 

 lb.) It coagulates by heat at about 68°-70° c. 



(c.) It exists in two conditions, analogous to those of haemoglobin ; 

 viz., hsemocyanin, and oxyhaemocyanin, the former being colour- 

 less, the latter having a blue tinge. 



{d.) Its absorption spectrum shows no bands, but only a cutting off of 

 portions of both ends of the spectrum. 



(e.) It contains a small quantity of copper, which seems to take the 

 place of the iron of haemoglobin. 



