JtNE 1, 1894.] 



KNOWLEDGE 



131 



limit of strength, but to have exceeded it, and to have 

 become stronger than before in the direction in which they 

 had been pulled. If the period of rest was materially 

 shortened, the restoration of strength was found to be 

 incomplete. 



Now let us consider how far fatii/m in this technical 

 sense is applicable to muscles as well as to metals. 

 Prof. Michael Foster, in his Cambridge University Rede 

 Lecture last year, pointed out that the muscles in the 

 leg of a frog severed from the body, and caused under 

 electrical stimulus to exert themselves in work until 

 thoroughly iccarifd, to use his own expression, and no 

 longer able to respond to the electrical excitement, will, 

 with rest alone, recover their elasticity and be able to 

 resume work as before. Prof. Foster demonstrated that 

 the weariness was in the muscle and not in the nerve. 

 These severed muscles were cut off from any new supplies 

 of strengthening material, and also from any replenishing 

 of vital force, and yet they recovered tone by rest alone. 

 It is therefore e\ident that this renewed vigour was 

 due solely to the readjustment or rearrangement of 

 molecules — to their recovery to a state of repose. The 

 worn tissues we know could not be restored, but fi'om the 

 fatigue the muscles did recover, and it is therefore clear 

 that the fatigue which we experience in our own bodies 

 must be largely fatigue in the technical sense in addition 

 to weariness proper, or worn->iess. Rest is therefore 

 required, not only to enable wasted tissues to be restored 

 by fresh material from the blood, and by the carrying 

 away of waste material, but also to afford opportunity for 

 the strained molecules to recover a state of repose. 



In iron or steel which has been strained, a more rapid 

 restoration of the molecules to a state of repose is effected 

 by heating to redness and cooling slowly. This process is 

 termed annealing, and is regularly adopted to take the 

 fatigue out of chains, the strength of which has been taxed, 

 and oitt of any piece or plate of iron or steel which has 

 been much mauled in getting it to shape. In copper, the 

 same result is accomplished by heating to redness and 

 quenching in water. 



If a piece of machinery is of ample strength for its work 

 it does not undergo fatigue, and is safe for any length of 

 time if not worn out by friction or by rust. In like 

 manner it is only those parts of our bodies which are too 

 light for their work which become reaMj fatigued. If one 

 is accustomed only to very Ught work, he becomes fatigued 

 when he undertakes heaner work. His muscles are 

 unfitted for it, and are consequently strained. In fact, all 

 heavy work is fatiguing, because our bodies are only fitted 

 for tlie average work of the race, and if heavy work were 

 to be done without excessive fatigue, special training 

 through many generations would be required. For work 

 only a little above the average, a course of training is 

 necessary. If, as in the case of machinery, the bodies of 

 men and animals were unprovided with a sensitive nervous 

 system to register fatigue and demand rest, we should 

 continually be having sprained and ruptured muscles and 

 broken bones. But some of the muscles, such as the heart 

 and the muscles of the chest used in breathing, although 

 in practically continuous action, are yet fairly equal to 

 their work, and unless exercised in an exceptional manner, 

 experience little or no actual fatigw. They, however, of 

 course, share in the drain of vital force which accompanies 

 fatigue and iieariness in any part of the body. It has been 

 pointed out that, although the heart appears to work 

 continuously, it really does its work expeditiously, and 

 finds time for a considerable amount of rest between the 

 beats, especially during sleep. The necessity for such 

 rest, however, is apparent, quite apart from any theory of 



fatigue in the technical senses, as the rest is evidently 

 required in which to repair the waste of tissue and of 

 unguent which must continually be going on. 



Prof. Foster further showed that if the severed but still 

 palpitating heart of a tortoise were washed with water 

 containing salt, some constituent of its strength would be 

 washed out, and the palpitations would cease, but that on 

 the application of a little lime-water the strength would be 

 restored, and the heart would again commence to beat. 

 Such recovery of tone cannot be due to the addition of 

 living cells such as might take place in the living heart 

 when incorporated in the living body, or the carrying away 

 of waste material, and can only result from change in the 

 muscular tissue, such as is involved in the absorption by 

 the impoverished molecules, through chemical affinity, of 

 their required nourishment. But such absorption is not a 

 property of muscular tissue alone. A similar process takes 

 place when iron becomes converted into steel by the 

 absorption of carbon in the case-hardening process. Strips 

 of iron can also be converted by this process into strips of 

 steel, their strength being about doubled. The iron is 

 simply heated and kept in contact with carbonaceous 

 matter until the absorption is complete. 



STAR CLUSTERS IN THE ^ ARGUS REGION OF 

 THE MILKY WAY. 



By A. C. Ranyard. 



THE great nebulous stream which stretches across 

 the heavens in the Northern and in the Southern 

 Hemisphere is far from being a uniform ring of 

 nebulosity spangled with stars. When different 

 regions of the Milky Way are examined in detail, 

 they are found to exhibit local peculiarities which are not 

 recognized on a survey of the heavens with the naked eye. 

 Such differences of nebulosity and stellar condensation 

 seem to indicate that the different parts of this immense 

 cosmical structure are not identical in constitution, or, 

 if we assume that the various chemical elements are 

 uniformly distributed in space, such a want of homogeneity 

 teUs a tale of vast differences in the conditions under which 

 the various parts of the galactic system have assumed 

 their present form. 



That the Milky Way is far from homogeneous was 

 distinctly recognized by Sir John Herschel during his 

 telescopic survey of the heavens, and now that, with 

 the aid of the camera, we are able to place accurate 

 pictures of different parts of the Milky Way side 

 by side for comparison, the characteristic differences 

 exhibited by different regions of the nebulous stream 

 become still more apparent. In speaking of the tj Argus 

 region of the Milky Way shown in our plate. Sir .John 

 Herschel (in the Cape Observations, p. 33) described it as 

 composed of stars of larger average magnitude than 

 other parts of the Milky Way, grouped into a series of 

 clusters separated by a number of darker patches and 

 lanes. In other parts of the Milky Way the nebulosity is 

 comparatively uniform ; in others, again, it is tlocculent, as 

 Sir .John Herschel described it, "like clouds passing in a 

 seud." The whole of the southern half of the Milky Way 

 appears to be rather more coarse-grained than the northern 

 half, and it is rather more thickly spangled with naked-eye 

 stars. 



Such differences of constitution in different directions is 

 alone sufficient to negative the supposition tha: the Milky 

 Way is the projection on the heavens of a stratum of 

 stellar condensation, which corresponds, as it were, to a 



