194 HOW TO WORK 



I think, by Professor Huxley for a membrana preformativa, which 

 does not exist in this situation. 



A Fibrous Appearance Produced in Structureless Membranes. 

 Clear, transparent, and apparently structureless membranes, when 

 pressed, torn, and twisted, have a fibrous appearance ; and delicate 

 vessels, whose coats are perfectly transparent when pressed and col- 

 lapsed, may be very easily mistaken for a form of fibrous tissue. Both 

 capillaries and fine nerve fibres may be mistaken for fibres of elastic 

 tissue. Indeed, capillaries uninjected and stretched, can only be dis- 

 tinguished from fine nerve fibres with the utmost difficulty. If any 

 doubt exist in such a case, it may always be cleared up by injecting 

 the capillaries of the part with a clear transparent material, like plain 

 size, or the transparent injecting fluids, recommended in pp. 93, 94 

 95, when, if the fibrous appearance is not real it will be lost; while 

 if fibres really existed, they would still be visible. The presence of 

 capillary vessels in a structure has been entirely overlooked in conse- 

 quence of their being collapsed and shrunken, in which state they 

 have been regarded as elements of the connective tissue. 



Collection of Oil Globules Appearing as if within a Cell. Oil 

 globules in fluid not uncommonly form small and nearly spherical 

 masses or collections, which become covered with a certain quantity 

 of mucus or viscid matter and granules, originally contained in the 

 fluid, so that the little intervals between the minute oil globules become 

 filled up. The outline of the mass is perfectly clear, and sharp, and 

 well defined, and from mere ocular examination it would be impos- 

 sible to say that the oil globules were not enclosed in a cell wall. 

 A consideration of the circumstances under which such structures 

 have been met with, will often assist us materially in determining 

 their real nature. Such " cells " may be prepared artificially without 

 the least difficulty, and in some cases it would not be possible to dis- 

 tinguish the artificially formed cell from the natural cell by micro- 

 scopical examination in water ; and the process of tinting, p. 107, 

 would only help us when the natural cells were quite fresh. It 

 need scarcely be said, however, that with respect to the formation of 

 these bodies there is no analogy whatever. Of the artificial cell the 

 most external part was last formed. It was deposited around a col- 

 lection of particles. But in the natural cell the outer part is the 

 oldest part. It was produced before the matter in the central part of 

 the cell was formed. Probably the only observer who still maintains 

 that living cells are formed by the aggregation of granules, is Dr. Hughes 

 Bennett, of Edinburgh, who also thinks that a bacterium is formed by 

 the coalescence of already existing particles. Dr. Bennett admits, 

 however, that such simple organisms multiply by division, and thus 



