BLOOD VESSELS IN OMENTUM OF YOUNG RABBITS. 243 



been so variously interpreted, it follows that there can be 

 nothing in its objective characters which is distinctive, each 

 observer deciding for himself as to its nature in accordance 

 with his preconceived ideas. 



I made, some time ago, a special study of the development 

 of blood-vessels in foetal and in inflamed tissue. I found that 

 when a mouse foetus, at the stage of development fitted for 

 the study, was placed in half per cent, solution of osmic acid, 

 and allowed to remain some hours in the solution, portions 

 of the integument, the cranial bones, and other tissues, could 

 be placed entire under the microscope, and examined in very 

 favorable circumstances. Such preparations are particularly 

 well suited for an examination of the nature of the conical 

 mass which projects from the previously formed vessels. The 

 results which I obtained in this manner can be stated shortly. 

 The conical mass is composed of amorphous matter between 

 the bundles of connective tissue. It refracts light differently 

 from the connective tissue itself, and stains differently from 

 either the connective tissue or any cellular element observable 

 in connection with that tissue or with the vascular wall. It 

 contains no nucleus, and its form is at no stage like that of 

 any known cell or part of any known cell, I can, therefore, 

 see no foundation for supposing it to be cellular. The large 

 nucleated blood-corpuscles of the foetus can be seen wedging 

 their way into it through the vascular wall, a thin, narrow 

 part of the blood-cell being Avithin the mass, and a large 

 spherical part of it being still within the vessel. It is fair to 

 assunie that an opening through which a blood-corpuscle can 

 force its way will permit the fluid plasma of the blood to pass, 

 and into the space represented by this appearance the blood- 

 plasma must have been passing in greater or less quantity. 

 It is in this plasma, rich in fibrinogenic material, that I find 

 an explanation of the conical mass which projects from the 

 capillaries. 



In osmic-acid preparations spindle-cells with large, some- 

 times multiple, nuclei can be seen in the walls of the space 

 in which the mass is contained. 



In fresh preparations, or preparations obtained by many of 

 the commonly used reagents, the nuclei alone of these spindle- 

 cells are seen, and the appearance is apt to suggest the idea 

 of a cellular structure. Osmic acid possesses the quality of 

 enabling us to see the spindle-cell as well as its nucleus, and 

 thus strips the space in which the cells lie, and into which 

 the blood forces its way, of all claim to be regarded as cellular 

 in its nature. 



In my studies on the foetal tissue of the mouse, I did not 



