CHANGES WROUGHT IN PATHOLOGY 133 



possess a characteristic, highly concentrated ground sub- 

 stance, connected with structures which represent, in 

 the main, thin layers deposited about the formative cells 

 or their delicate protoplasmic extensions. A very in- 

 structive example of this kind is furnished by the exceed- 

 ingly hard cartilage of myxina, in which SCHAFFER was 

 recently abl^ to demonstrate layers of great delicacy sur- 

 rounding the cartilage cells. In such thin precipitation 

 layers there can arise, when they absorb or gradually 

 give off water, tremendous pressures which might well be 

 of great importance in hardening the entire mass. Ac- 

 cording to experiments which I have carried out in conjunc- 

 tion with Dr. LUDWIG MACH, it is an easy matter to give 

 protein a bony hardness by pressing it into a steel tube 

 and heating it almost to its decomposition temperature. 

 Interestingly enough, this ability to form a material 

 sufficiently hard to be worked with instruments is con- 

 nected with a certain integrity of the albuminous sub- 

 stance and is lost entirely when the albumin is decomposed 

 beyond the albumose stage. By mixing with the protein 

 the fine dust of insoluble calcium salts in the proportion 

 in which these are found in bone, the solidity of the prod- 

 uct can be markedly increased. 



The pressures exerted by thin layers of colloid under 

 suitable circumstances cannot well be determined. That 

 these may attain high value is shown by experiments of 

 CAILLETET, who was able to render glass permanently 

 doubly refracting through thin layers of gelatine which 

 were allowed to dry upon its surface. 



With this example, to which many others might be 

 added, illustrating the connection between physico- 

 chemical investigations and morphology, I shall close 



