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ZlK Ibuman Shin : 

 3t6 Structure an& jfuuctione/' 



By Arthur J. Hall, B.A., M.B. (Cantab.); 



Physician, Sheffield Public Hospital; Lecturer on Physiology, 

 School of Medicine, Sheffield. 



HA\ E chosen this subject for my lecture to-night 

 for several reasons : one is, that it can be considered 

 more quickly as a whole than many physiological 

 subjects, though, in the brief space at my disposal, 

 it is impossible to give more than the barest out- 

 •((*/^|a^V line ; another reason is its importance to health ; 

 ^^V\\^?^ ^ third IS that there are so many erroneous ideas 

 x^|^7 about its structure and functions. I feel that in 

 dealing with this subject I must commence by 

 referring to a few physiological axioms, as it will save much expla- 

 nation afterwards. You are all acquainted with the meaning of 

 the term "Cell," as connected with living things. Briefly, the 

 definition of a cell is a "Microscopic portion of living matter or 

 protoplasm having a distinct life history of its own." It is, in fact, 

 a little mass of living material which is practically, as regards its 

 life history, distinct from everything around it. Of such a typical 

 cell we have an example in that low form of water-life, the Amoeba. 

 This creature is unicellular ; that is, it consists of one single cell, 

 just as every human being once consisted of a single cell, the 

 Ovum. This minute Amoeba, which is more like a speck of jelly 

 than anything else, is yet an individual being, and goes through 

 its life-history as essentially separate from other Amoeba as you or 

 I go through ours. From the moment that it is born from a parent 

 Amoeba it has to obtain, eat, and digest its own food, grow to 

 maturity, move about, reproduce its species, decay, and die as 

 certainly as any human being, and, as a rule, with far more regu- 

 larity of habits. 



If, however, we ascend the scale of living things, we find that 

 the members of the series become more elaborate in their structure. 



* A Lecture delivered before the Sheffield Micro. Society, Feb. lo, 1893. 



International Journal of Microscopy and Natural Science. 



Third Series. Vol. III. s 



