^Cmlji™^ and Microscopic Physics. ' 19 
dead matter. The hypothesis that every living thing comes from 
an egg has given way to another — every living thing comes from 
a cell.* Probably we shall, in due time, find under what conditions 
cells are first formed, and thus the lower forms of hfe created. 
But a few years since the question " What is heat ? " would 
have puzzled the greatest philosopher ; now, thanks to Dr. Tyndall's 
valuable work, hundreds of school-boys could answer it. 
The problem of the conditions of cell-life is peculiarly a problem 
for microscopists. Surely much may be hoped for, from their 
known perseverance and ingenuity, notwithstanding the apparent 
insolubility of the problem. 
It has been stated that crystals never form curved lines. This 
assertion is not strictly true. 
A point of great importance in this connection is that Mr. 
Eainey has found that when a solution of a hme-salt in gum- 
arabic is slowly decomposed, carbonate of lime is deposited in 
spheroidal concretions. Sometimes two of these will unite and 
form a dumb-bell ; occasionally a number will unite in the form of 
a mulberry. According to Dr. Carpenter, similar concretionary 
spheroids are common in the urine of the horse, in the auditory sacs 
of fishes, in the skin of the shrimp, and other imperfectly calcified 
shells of Crustacea, as well as in certain imperfect layers in the 
shells of moUusca. 
Again, it has been stated that carbonate of Hme is not deposited 
in animal substances in the crystalline form. Dr. Carpenter says 
that the external layer of an ordinary egg-shell consists of a series 
of polygonal plates resembling a tesselated pavement. 
Professor Williamson says that there can be no doubt that the 
calcareous deposit in the scales of fishes is formed upon the same 
plan. 
Want of space alone prevents me from adding other examples ; 
but from the instances I have given we may see that the presence 
of organic matter is often sufficient to prevent the deposition of 
lime in a crystalline form, and to cause it to assume a circular 
form, either in or out of a hving organism ; while in the second case 
we find that vitality does not prevent the deposit of Hme in the 
crystalline form. 
In a very suggestive speech Mr. Slack referred to the triumphs 
of modern chemistry — the building up of highly organized sub- 
stances — synthesis. Dr. Beale objected that no parallel could be 
fairly drawn here, because the method by which the highly 
organized substances are produced naturally is so exceedingly 
* Even this proposition is extremely questionable. It is certainly unfounded 
if the current definition of the word " cell " be accepted. Absolutely it resolves 
itself into this : that living things proceed from a substance which may —following 
Prof. Huxley— be very fairly though generally styled Protoplasm. — Ed. M. M. J. 
C 2 
