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Mr. B. Lewis on the Lymphatic 



[June 21 , 



senile atrophy, to mere shrinking of the ceil from degenerative changes, 

 and the production thereby of an artificial fissnre or chasm around the 

 cell. The broader views .now advanced will enable such observers to 

 expect similar appearances from very diverse causes. 



The unusual distinctness with which these lymph-sacs sometimes pre- 

 sent themselves may, I am convinced, be occasioned by hardening agents, 

 such as chromic acid and its salts ; but I feel equally well assured that 

 similar appearances may result from an unusually distended lymph- 

 system. We may therefore expect to find them well shown where obstruc- 

 tive agencies interfere with the outflow of the lymph-stream towards the 

 pia mater. The large size and defined contour of these lymph-sacs in 

 senile atrophy of the brain may undoubtedly be due to shrinking of the 

 enclosed degenerating protoplasm of the cell ; yet the important point 

 is to recognize these spaces as natural structures in an unnaturally dis- 

 tended condition, for their large size appears to me due not only to 

 wasting and recession of the enclosed cell, but to a large accumulation 

 of lymph, the lymphatic channels, both pericellular and perivascular, 

 being in a distended condition throughout. 



Sections from the frontal lobe of a young and perfectly healthy cat ex- 

 hibited these pericellular spaces with remarkable distinctness (vide Plate 1. 

 fig. 1). In this instance the distension of the lymph-sac was probably 

 accompanied by a general plethora of the whole lymph- system of the 

 brain, as the appearance of the nerve-cell would scarcely warrant the 

 supposition of the appearance being entirely due to the shrinking of the 

 cell consequent upon chrome hardening. The morbid conditions interfering 

 with the perivascular lymph-current of the brain are numerous. Hyper- 

 emia acts in this way and greatly modifies the nutritive and depurative 

 changes proceeding in the pericellular sacs. Deposits within the peri- 

 vascular sheaths, aneurismal dilatations along the vessels, tubercular out- 

 growths from their walls, proliferating connective elements, may all in 

 their turn affect very materially the free exit of lymph from the peri- 

 vascular channels, which is a sine qua non for the maintenance of the 

 functional activity of nerve-cells. 



The proliferation of the connective elements of the neuroglia is represented 

 in Plate 2. figs. 5 and 6, the latter being a fresh-teased preparation, while 

 the former is from a section obtained by means of the freezing microtome. 

 The truly protean forms assumed by these connective elements are well 

 seen in such specimens, the nucleated corpuscle becoming swollen, cloudy, 

 and often coarsely granular ; at other times it maintains through all its 

 changes of form the pellucid delicate appearance of its protoplasm. 



Methods of Examination of the Cortex Cerebri, 

 It will be necessary for me to dwell shortly upon the methods employed 

 by myself in this investigation. I have not limited myself to any con- 

 ventional process for obtaining sections ; but, whilst making free use of 



