The Physical Nature of the Lipid Globules in the Living Neurones of Helix aspersa as indicated by Measurements of Refractive Index

The lipid globules in the neurones of Helix aspersa have been found by Chou in 1957 to be of three distinct kinds that differ from each other in chemical composition. In the present investigation, the refractive indices of these three kinds of globule were measured by the technique for measuring the refractive indices of cytoplasmic inclusions in living cells developed by Ross in 1954, which is here described in detail. It was found that the refractive indices of the globules containing mixed lipids and proteins and those that probably contained triglycerides alone, all had relatively high refractive indices of about 1 47-1 -50. These values are comparable with the known refractive indices of many pure lipids. The refractive indices of the globules containing phospholipid were much lower, being about 1-41-1 42, which is lower than that of any pure lipid. This indicates that these globules probably also contain appreciable amounts of water associated with the phospholipid molecules, as was suggested by Schmidt in 1939. The results also show that refractive index measurement made in conjunction with histochemical investigations may, in some cases, provide useful additional information about the physico-chemical nature of cell constituents.