Bauhaus-Universität Weimar

metry has arrived, and the use of good instruments, have made us 
now so well acquainted with the physical properties of the organic 
tissues, that we are enabled to refute the above theory, by merely 
comparing with precision the size of different parts. 
Microscopic examinations, if intended to serve as the basis for 
scientific researches and comparisons, must not ponsist merely in the 
direct measurement of each object; a much more important and 
essential mode of investigation is the comparison of the object to be 
measured with some other body that can be taken as a standard. 
Thus, for instance, in measuring the size of the muscular or nervous 
fibrils, they should be placed under the microscope, together with 
red particles of human blood, and both should then be observed at 
the same time. The admeasurements of the red particles of human 
blood, as stated by Kater, Wollaston, Prévost and Dumas, Weber, 
Wagner, and myself, agree so nearly, that their diameter may with 
great certainty be stated at ^qW of an inch English. We have thus 
a certain standard of measurement. As standards of comparison, I 
employ the red particles of human blood, easily obtained by slightly 
scratching the skin, those of frog’s blood which are about four times 
larger in diameter, and the nuclei of these latter bodies, obtained 
by the action of acetic acid, which measure about ^th or èd the 
long diameter of the entire red particle. We have already seen, (at 
pages 20-21,) that the ultimate fibres of muscles and nerves do not 
correspond in size either with the red particles or their nuclei. 
Moreover, the nuclei of the red particles of the frog’s blood are 
not globular but elliptic in form, and those of the red particles of 
the salamander’s blood are even flattened. How, then, can they 
compose the ultimate fibres of nerves and muscles? We shall see 
that the form of these tissues affords no grounds for such an opinion. 
And the recent observations of Schwann and others, on the mode 
of growth of all the elementary parts of the body, prove it to be 
The most minute capillary vessels do not ramify upon the primi¬ 
tive fibrils of nerves and muscles; these fibrils are too fine to receive 
vessels, and are, in fact, more minute than the capillary vessels them¬ 
selves, which measure from jg^g to T-gi-g of an English inch in dia¬ 
meter. Nutrition, therefore, must be effected through the coats of the 
capillary vessels, and the process consists in the fluid parts of the 
blood permeating the parietes of the capillaries, while the solid par¬ 
ticles are visibly carried onwards into the veins. The most important 
materials for nutrition are the albumen and fibrin dissolved in the 
liquor sanguinis. A portion of these matters permeate the parietes 
of the capillaries, and are imbibed by the tissues; and what is effused 
over and above the quantity required for their nutrition, is taken up 
by the absorbent vessels, and carried again into the blood. It is 
here of importance to know that the capillaries really have solid 
parietes; the proofs of which were seated at page 224. Nothing 
can pass from the blood to the tissues, or from the tissue to the blood, 
without permeating, in the fluid state, the walls of these vessels. 
The hypothesis of the blood flowing in simple canals excavated in


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