526 PHILOSOPHICAL TRANSACTIONS. [aNNO 1721. 



appeared larger than the portion of fibres. By which one may easily imagine, 

 in how small a space that number of fibres is comprehended, each of which 

 consists of so many vessels. 



I likewise made observations on the muscular fibres of a pike, a roach, char 

 and flounder, in each of which I found the fibres to be composed of small 

 vessels, like those of a cod and pearch. The fibres of a sprat too were but 

 little thinner than those of the large pearch, and the vessels of which the fibres 

 were composed, were nearly as numerous as in the fibres of the pearch. 



From these observations some persons may be apt to conclude, that the 

 muscular fibres of land-animals are of the same thickness with those of fish. 

 But for the satisfaction of those who have not seen the objects here spoken of, 

 I have caused a small portion of the muscular fibres of a large ox to be deli- 

 neated, as they appeared through the same microscope with the former, to 

 show the thickness of the dried fibres, and the vessels that compose them, as 

 is represented in fig. 15. In the transverse section of one of these fibres, were 

 counted 25 vessels in one fibre. 



On cutting some of the muscular fibres of a small smelt transversely, I 

 placed them before a microscope, and saw not only that these fibres were twice 

 as thick as those of an ox, but likewise that they were provided with as great a 

 number of vessels as the fibres of other fish. 



On thus observing that the muscular fibres of fishes were much larger than 

 those of beasts, I began to consider, for what reasons there was so great a dis- 

 proportion between them. But all the satisfaction I could meet with was, that 

 as fish swam in the water, their muscular fibres need to exert very little force, 

 in order to support their bodies in it, because they are very nearly of the same 

 specific gravity with the element in which they swim. All the force they exert 

 is in their progressive motion, in pursuit of their food. Whereas the muscular 

 fibres of land-animals exercise a great force, not only in supporting and moving 

 their own bodies, but in carrying burthens and other labour they are put to. 

 And we must allow, that the smaller and finer the fibres are, to make a 

 body of any determinate thickness, the stronger will be the composition, and 

 therefore the muscles in flesh must be stronger than those of fish. 



Taking out a little of the mealy substance of a boiled grey pea, I laid it 

 before a microscope, where it appeared to consist of such like parts as are 

 found in rats dung; every one of which parts consisted of a great number of 

 very small particles; but could not discover any membranes enveloping those 

 parts; from whence I concluded, that those membranes were destroyed and 

 dissolved by the hot water. On this, I took another grey pea, which had not 

 been boiled, and cut it into very thin slices; when I not only saw the mem- 



