1892.] MICllOSCOPICAL JOUENAL. 9 



Motile Bacteria \vith special reference to the Staining Processes. Amer- 

 ican Monthly AIicrosco/>ical Journal (1S91), p. 15. 

 13. Afi'ssra, A. Contribuzione alio studio delle Ciglia dei batterii e proposta di 

 una classificazione. Rivista (Vigienee sauita fublica. No. 14(1889), 

 P- 513- 



Iiitroductiou to Elementary Biology. 



By henry L. OSBORN, 



HAMLINE, MINN. 



Part VII. — A Specific Lifk History Considered Biologically. — 



The Frog. ^ 



(^Continued from p. 2^j, vol. xii.) 



We have now seen that the skin and the lining of the month of the 

 frog present in their strncture and actions as at present nnderstood no 

 conditions which are absolutely unique and vmlike the structure and ac- 

 tions to be found among the protozoa. Undoubtedly the fimctions of 

 these various cells are more complex than we have had time to indi- 

 cate ; thus the ciliated cell has all the ordinary work of cell life and the 

 work of moving cilia besides, but it seems enough to confine our atten- 

 tion to the special functions of the cells in the present sketch, it being 

 understood, however, that we could readily trace in all the activities 

 parallel ones in the protozoa. We see that the pigment cells specialize 

 two powers — metabolism for the production of pigment, and motion for 

 color changes ; while the ciliated cell specializes the power of motion 

 in another way. 



The power of motion is further specialized in two ways in the frog 

 in cells of the true " muscular tissue." In Amoeba the contractility is 

 not increased in a definite manner over certain tracks, as it were, which 

 from habit and inheritance become easy and very readily operated on. 

 In the stem of Vorticella the muscular fibre acts quickly and definitely. 

 Presumably its action is helped to be so very quick in response and 

 vigorous from the effects of use, for we should expect practice to im- 

 prove here as elsewhere. If in the frog masses of elongate cells, whose 

 substance is being constantly used for contractions, are so placed that 

 the shortening can take place simultaneously and all in one direction, 

 their actions can be summated into a pull of an extent determined by 

 the number of the cells, in part at least. It is in this way only that we 

 can understand the anatomy and physiology of frog's muscle, striped 

 or unstriped. We have a good view of the unstriped muscle in some 

 of the small arteries, as, for instance, those of the mesentery, when they 

 can be prepared very readily for examination by first staining with 

 borax-carmine, then mounting in balsam or glycerine. The small artery 

 is seen to be clasped by rows of spindle-shaped cells, involuntary 

 muscle cells, which wrap themselves across the artery. These cells, 

 if they are stimulated by nerve stimuli must shorten and broaden their 

 shape, and in shortening they must narrow the circle of whose arc they 

 form a major part ; so all the cells working in unison in a large area 

 upon the bores of the small arteries, the capacity of the area for blood 

 is lessened and the part loses blood, or, as we say, becomes pale. In 

 this case it is the muscular coat of the artery which is at work, but this, 

 to mean anything biologic, must be equal to saying that the spindle- 

 shaped cells of tissue which have specialized the power of contractility 



