Muscular and Pulmonary Tissues. 351 



tionally to their respective volumes. Should a jelly be prepared 

 consistiug of a mixture of a solution of isinglass and white of 

 Q^^, it will exhibit^ v^^ith reference to the albumen it contains, 

 diffusible properties entirely at variance with those observed in 

 the case of the mixture of jelly and salt. When water is 

 poured over this albuminous jelly, the albumen will not diffuse 

 out, or its diffusion will be extremely slow ; hence a jelly con- 

 taining albumen has such a thorough hold upon it that this sub- 

 stance can no longer be extracted from the jelly; no amount of 

 trituration or pounding or washing will separate the albumen; 

 this simple want of diffusibility caused the albumen to become 

 firmly united with, or fixed by, the isinglass jelly. 



Graham has observed that, as a rule, substances possessed of 

 the property of crystallizing (such as common salt or sugar) 

 yielded solutions much more diffusible than those of substances 

 which were not possessed of the power of crystallizing, such as 

 gelatine ; hence he has classed substances into crystalloids and 

 colloids. 



How can we explain these phenomena, unless it be admitted 

 that there existed a degree of attraction or adhesion between the 

 albumen and the jelly greater than that occurring between the 

 salt and the jelly — -so that in the one case the albumen was fixed 

 in the jelly, while in the other the salt moved freely out of it ? 

 Substituting the simpler cases of pure white of egg and a solution 

 of common salt in water, the different degrees of diffusibility exhi- 

 bited in these two instances will admit of a similar explanation, the 

 water retaining the albumen in one case, and letting out the 

 salt in the other. If this view be taken of the cause of the 

 various degrees of diffusibility of different solutions, it must be 

 acknowledged that there exists a certain attraction between 

 substances and the water which holds them in solution ; and this 

 attraction varies in its degree according to the substance. 



I propose, for want of a better denomination, to call this by 

 the name of colloid attraction, and to say that the albumen in 

 white of Q^^ is held to the water by " colloid attraction.^' I 

 therefore retain the names colloid and crystalloid given by 

 Graham — colloids not being possessed of the power of crystal- 

 lizing, and being sparingly diffusible, while crystalloids are 

 crystallizable substances, yielding readily diffusible solutions. 



Crystalloid solutions never gelatinize ; colloid solutions either 

 gelatinize or solidify into a thick, gumm^y, adhesive substance, 

 which dries into a residue exhibiting, frequently, somewhat the 

 appearance of a varnish. 



This colloid attraction, v/hich keeps water and isinglass 

 united together in a jelly, is also apparently concerned in the 

 formation and physical existence of animal tissues. Muscular 



