382 MACROPHAGES FROM ARACHNOID CELLS. 



same convincing clearness, as one finds on the thin connective-tissue trabeculse 

 uniting the arachnoid membrane to the pia mater. 



The cells clothing the trabeculse are very sensitive to changes in the cerebro- 

 spinal fluid which bathes them. Weed (1917, p. 467) calls attention to this fact by 

 remarking that the "general morphology * * * depends apparently * * * on their 

 physiological state." Particulate matter, either resulting from cell destruction or 

 introduced directly into the cerebro-spinal fluid, calls forth a most remarkable reac- 

 tion. Inert particles, such as carbon or cinnabar, as well as active matter, such as 

 fragmented red blood-corpuscles or dead leucocytes, initiate morphological changes 

 in the arachnoid cells. The reaction of the cellular membrane to such participate 

 matter is a slow one and appears to be well under way only after the first 24 hours; 

 dead bacteria may be taken up and removed by the leucocytes before the arachnoid 

 cells show any signs of activity. The most striking results have occurred after 

 stimulation with laked blood, due probably to the fact that it has no toxic effect 

 on the cells and may be utilized by them as food. Partial laking with distilled 

 water was resorted to because the red blood-cells seem to live for some time if in- 

 jected immediately into the subarachnoid space, whereas laked corpuscles cause 

 a very much more rapid response on the part of the arachnoid cells. This fact 

 suggests a degree of protection against phagocytosis by the living erythrocyte. 



The blood was prepared for injection with due precautions to keep it sterile. 

 Twenty cubic centimeters of blood, either homologous or autogenous, were defibrin- 

 ated by shaking up with glass beads. If massive doses of erythrocytes were desired 

 the defibrinated blood was centrifugalized, and subsequently the isotonicity of the 

 mixture was restored by adding 10 X normal concentration of sodium chloride, 

 potassium chloride, and calcium chloride. One or two cubic centimeters could be 

 slowly injected into the lumbar subarachnoid space, or (if a heavy dose were desired) 

 a replacement of the cerebro-spinal fluid over the cord was done in the following 

 manner: A needle was introduced through the occipito-atlantoid ligament and one 

 into the lumbar subarachnoid space. Laked blood was allowed to flow by gravity 

 into the lumbar needle while the displaced fluid made its escape from the occipital 

 region until laked blood appeared. In this way one gets possibly 5 or 6 c.c. of 

 corpuscles around the spinal cord, and if the irrigation pressure is maintained below 

 300 mm. of water the animal never shows any symptoms referable to the experiment 

 when once it recovers from the anesthesia. The various steps were controlled bac- 

 teriologically to rule out a possible confusion with a septic meningitis. 



Within 6 hours after the hemolyzed erythrocytes are introduced into the 

 subarachnoid space a full-blown sterile meningitis is in progress; 6,000 to 10,000 

 leucocytes, composed almost entirely of the polymorphonuclear and transitional 

 variety, are present in a cubic millimeter of the blood-tinged cerebro-spinal fluid. 

 Examined on a warm stage these leucocytes exhibit a most surprising amoeboid 

 activity and their cytoplasm is literally stuffed with the small particles of frag- 

 mented red blood-cells. At the end of 24 hours the leucocyte count in the spinal 

 fluid has dropped to 2500-1500 per cubic millimeter and in 48 hours has reached the 

 neighborhood of 100. With the decrease of smaller cells from the fluid a new 



