1882.J 



MICROSCOPICAL JOURNAL. 



38 



^ast dangerous, and only local in its 

 external manifestations. Yet this mild- 

 er form of the disease is a protection 

 against the more malignant type. 

 Upon this fact depends the efficiency 

 of vaccination. The disease produced 

 by vaccination is a mild form of 

 small-pox. The results of recent in- 

 vestigations leave no reasonable doubt 

 of the protective influence of vaccin- 

 ation, and, while there are always a 

 few headstrong and conservative in- 

 dividuals in every profession, it is 

 not strange that there should still be 

 a very limited number of physicians 

 who oppose vaccination as a useless 

 proceeding. But there are not two sides 

 to this question, and it must be the 

 opinion of every person who will 

 study the subject with care, that the 

 welfare of the community requires 

 that vaccination should be made 

 compulsory. 



Upon every leaf and flower, in the 

 air and in the water, from the regions 

 of eternal snow down to the bottom 

 of the deepest seas, the simplest 

 forms of life are found. Among these, 

 wherever they may be, the struggle 

 for existence is incessant, and one 

 has only to make use of a microscope 

 to see the fight in progress — battles 

 which, in miniature, portray the great- 

 er conquests of beasts and men which 

 have resulted in the present condition 

 of development. 



Within the microcosm of a single 

 drop of stagnant water, may be found 

 myriads of living forms of curious 

 shapes and strange habits, all mani- 

 festing the powers of growth and re- 

 production in the simplest form. 

 Higher in the scale the processes of 

 life become more complex, gradually, 

 as development proceeds, we see 

 a differentiation of the cellular 

 structures, so that cells subserving 

 special purposes become distinct from 

 the others, and this distinction be- 

 comes more and more defined as we 

 go still higher, until finally the speci- 

 alization of function results in the 

 perfection of each organ for its work, 

 and in the mutual interdependence of 



the parts which constitute the perfect 

 whole. It is this specialization and 

 adaptation that marks the essential 

 distinction between the simple and the 

 complex forms of life. It is a striking 

 thought that all the functions of the 

 human body have their counterpart 

 in the structureless amoeba. Yet it is 

 more than a suggestion of fancy, since 

 biology teaches that the development 

 of all forms is a result of the division and 

 the gradual differentiation of simple 

 cells. The changes in the forms of 

 animals, which have been gradually 

 brought about in the struggle for ex- 

 istence, the adaptation to surrounding 

 circumstances and the survival of those 

 best fitted to withstand the conditions 

 about them, have progressed through 

 unnumbered centuries, until the ex- 

 isting forms of life have become what 

 we find them. As the geologist reads 

 the story of the world's long history 

 on the leaves of solid rock, and there 

 finds the record of its gradual evolu- 

 tion, through sudden catastrophes or 

 the more slow and steady action of 

 other influences still at work, wearing 

 down the mountains and filling seas 

 and valleys, so the embryologist 

 can trace the results of the environ- 

 ments of centuries in the animals 

 of to-day. For all the changes 

 of form which have resulted in 

 the perfect animal as it has 

 slowly developed and been modified 

 by external conditions, have left 

 their records upon the germ, so 

 that all the great features of its past 

 history are revealed in the course of 

 its embryological development. The 

 modifications which were only brought 

 about through the changes of the ge- 

 ologic ages, are again passed through 

 in embryonic life, in the course of 

 hours or days. This potency of life 

 must first be latent in the microscopic 

 germ — the single cell from which 

 all living creatures spring — and 

 while in the beginning these seem to 

 be all alike, while many of them 

 proceed in parallel lines as they de- 

 velop, yet each one with a strange 

 certainty, reproduces its parent form. 



