2 Journal New York Entomological Society, [^'o'- >^>^\'I- 



of blood which oozes forth is caught on a sterile cover slip. The 

 cover slip is then placed over a sterile depression slide, and the edges 

 are sealed with melted vaseline. 



Insect blood cells grow^ very well in their own plasma, but Locke's 

 solution can be added if desired. Locke's solution is isotonic with 

 insect tissue, but has no particular advantage except that its addition 

 thins out the plasma and produces a greater transparency in the prep- 

 arations. 



If we carefully place the drop of blood in the center of the cover 

 slip the cells grow very slowly. Many disintegrate entirely, and others 

 do not show any visible growth for two or three weeks. ' Even the^i 

 no large syncj-tial masses are formed, and sooner or later, as soon as 

 the supply of oxygen in the depression slide is diminished, begin to 

 disorganize. At first I supposed that the death of the cells was due 

 to the exhaustion of the required nutrition, but such was not the case. 

 Insect blood cells can be kept alive for a surprisingly long time with- 

 out the addition of fresh media. If the preparation, in which the cells 

 are disintegrating, is shaken a bit so that the drop of blood flows 

 over along the edges of the cover slip a change will soon become ap- 

 parent. On reexamination after about two or three weeks the cells 

 lying in close proximity to the vaseline will appear healthy, and beau- 

 tiful large syncytial masses will be found. 



In order to be certain that the vaseline was not giving off some- 

 thing which stimulated the cells to grow, the following experiments 

 were performed : Blood was placed in the center of the cover slips and 

 a small piece of sterile vaseline added to each drop. Six such slides 

 were prepared, but I failed to notice any large syncytial masses even 

 after six weeks. The preparations were then shaken so that the blood 

 flowed over along the edges of the cover slips and in two to three 

 weeks more the syncytial masses were obtained. 



We can conclude from these observations that direct air is abso- 

 lutely necessary for the growth of insect tissue. The blood cells kept 

 in the center of the cover glass soon exhaust the oxygen present and 

 cease to grow. However, if they are brought in contact with the 

 vaseline through which the air undoubtedly filters, they become reju- 

 venated and form syncytia. Of course air filters through the vaseline 

 also when the cells are confined to the center of the cover slip. Init it 

 is not so readily nor so rapidly obtained l)y the cells. The latter are 



