Physical Chkmistrv ani» Yetkrinary Scikncr. 1,h3 



of the non -electrolytes increases corresponding to a decrease of the 

 number of ions. 



Piroplasniosis is a disease of the red blood corpuscles, and the 

 presence of their decomposition products in serum and urine causes the 

 above-mentioned variations of the osmotic concentration. As long as 

 these products of thc^ hi>?moh'sis are colloidal they are osmotically 

 inactive, and only affect the conductiv ity of the serum in a negative 

 sense (they are obstacles to the migration of the ions). When the 

 decomposition proceeds they become crystalloid, and influence the 

 osmotic pressure in a positive sense. 



Horse-sickness, however, is a disease of the endothelia, and does 

 not greatly alter the concentration of salts. There was only a very 

 slight and not quite distinct decrease of A and A. It is therefore 

 possible to distinguish these diseases by cryoscopy, or better b}'^ the 

 examination of the conductivity. 



A very large number of examinations of the depression of freezing- 

 point and conductivity of cow's milk was made by Schnorf. He stated 

 that in all cases of sick milk glands the conductivity was super-normal, 

 and that it was therefore possible to recognise a disease of the mamnue 

 by this method alone, whilst the depression of the freezing-point is very 

 often, although not always, greater than normal. 



IV. COLLOIDS. 



(a) Gknkral. 



With very few exceptions the liquid components of the organisms 

 are not pure homogeneous watery salt solutions, but heterogeneous 

 systems, since the proteids are nf>t dissolved, but are colloidal. Col- 

 loidal solutions are combinations of water with one or several liquid or 

 solid substances veiy finely disseminated in it (emulsion colloids, sus- 

 pension colloids). The general characteristics are the following : they 

 have no defined critical points (boiling, freezing, melting point) ; in 

 other words, they do not alter the critical points of the solvens ; they 

 are obstacles for chemical reactions, because they easily absorb each 

 other and also salts ; their electrical transport (kataphoresis or con- 

 vection) either to the positive or negative electrode proves their elec- 

 trical charge. They are generally sensiti\e to electrolytes and colloids 

 with the opposite electrical signs, and a large number also to high 

 temperatures. 



Following the leading conception of the colloids as heterogeneous 

 sj'stems, and analysing, we can make the following statements : — 



(1) The particles must be so fine that the adhesion to the medium 

 is stronger than the gravitation, so that they do not follow the latter. 

 They are ultra-microscopic. As a matter of fact, with the ultramicro- 

 scope of Siedentopf and Zsigmondy colloid particles with diameters as 

 low as 0'006^ were observed, and so the heterogeneous nature of col- 

 loids could be proved. 



