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♦ KNOWLEDGE ♦ 



[August 1, 1889 



In late years mitigation of the virus of other diseases 

 has been accomplished by repeated cultivations. Anthrax 

 was firstly so mitigated by Professor W. S. Greenfield. 

 M. Pasteur afterwards made similar investigations on 

 anthrax. While Professor Greenfield was mitigating the 

 anthrax bacillus, M. Pasteur was doing the same with fowl 

 cholera, and published his results at about the same time. 

 The bacteria of acute pneumonia also have their virus rapidly 

 weakened by successive cultivations. Later still are the 

 results of Pasteur in mitigating the virus of hydrophobia. 



We now come to the consideration of the last part of our 

 defences, i.f., the ways of safe retreat. The first great thing 

 is to get fresh air. The proper ventilation of our houses is 

 now well known to be an absolute necessity for the main- 

 tenance of health, and it is a subject directly connected 

 with the bacterial question. For when we ventilate our 

 houses we not only get a fresh supply of oxygen and get rid 

 of carbonic acid gas, but we at the same time get rid of the 

 dusty and bacteria-laden air that is found in crowded locali- 

 ties. But even the best arrangement of ventilation is not 

 sufficient in crowded woi'kshops ; this, however, can be 

 remedied by those who live in such places taking a few 

 hours of vigorous outdoor exercise daily. The exercise 

 should be vigorous, so that the stagnant air in the lungs 

 may be got rid of, and that the lungs may be well dilated 

 with fresh air. The necessity for this is greater in men 

 with big chests. The lungs of such men when they do not 

 have proper exercise are not fully dilated, and are apt to 

 become contracted and unhealthy at the apices, thus leaving 

 a convenient place for the insidious attacks of the tubercle 

 bacillus. The truth of the above statement is painfully 

 exemplified in the case of shopmen who are confined in 

 shops, often ill- ventilated, and who have no proper time for 

 d.iily exercise excepting Sundays, when they are often too 

 tired to take advantage of a day with few outdoor atti'ac- 

 tions. It is here that we very frequently find victims of 

 consumption. It is also an important matter that we should 

 be able to occasionally leave the town for a week or two in 

 order that we may recruit our strength and repair any 

 point in our defences that may be weakened by the foe's 

 attack, and of course this can be done more thoroughly 

 when as few of the enemy are about as possible. 



There are some people who should never live in crowded 

 towns. I refer to those belonging to consumptive families. 

 We have all heard of hereditary consumption ; it is, how- 

 ever, extremely doubtful whether a child is ever born con- 

 sumptive ; the evidence goes to show that children are 

 born with a tendency to tuberculosis, not with the disease 

 actually existent. Such people should live in a mild 

 climate, a climate as nearly uniform as possible and in 

 country places, better by the sea. By this and by living 

 regular lives, the chances of the disease may be decreased. 

 Of coui-se there are immense difficulties in finding the above 

 ways of retreat. How can the majority of mankind get 

 away for holidays in the country ? How can they get 

 regular exercise in fresh air 1 The sooner the above 

 problem can be solved the better for the health, the happi- 

 ness, and for the morality of the race. For when our 

 bodies are diseased, the cells of our brains cannot act 

 properly, and the strength of our minds depends upon the 

 vigorous action of the little cells of which the active parts of 

 our brains are composed. 



Miss C. W. Bruce, of New York, Iws presented lifty thousand 

 dollars to Harvard College Observatory, which the director. Professor 

 E. C. Pickering, proposes to spend in the purchase and endowment 

 of a photographic telescope of 24 inches aperture. The object 

 glass will be a compound lens of the form used by photographers, 

 and known as a portrait lens. This form of lens permits of a short 

 focus, and gives a large field with good dcliuition. 



THE GREAT NEBULA IN ANDROMEDA, 

 31 MESSIER. 



IN the opposite page is a photographic re- 

 production, enlarged about three diameters, 

 from the best negative which Mr. Isaac 

 Pioberts has taken of the Andromeda 

 Nebula. It .shows a good deal more detail 

 in the outer parts of the nebula than can be 

 traced on the enlargement published with 

 the March number of Knowledge, which is on a smaller 

 scale. 



In the picture which we now offer to our readers the 

 nebulous masses breaking up into clusters of nebulous points 

 or small stars which lie along the outer whorl of the great 

 nebula are well shown, and 

 the stellar centre of the small 

 elliptic nebula H.V. 18 is just 

 traceable. All three nebulas 

 (.31 Messier, .32 Messier, and 

 H.V. 18) have stellar centres, 

 but the central parts of the 

 great nebula are entirely lost 

 in the enlargements. On the 

 original negative there are 

 some curious dark patches 

 and branching channels in 

 the neighbourhood of the 

 inner dark spiral and on 

 the more central parts of the 

 nebula. Some similar dark 

 patches or markings can be 

 seen in the enlargement to 

 the north of the small nebula 32 Messier, and at the north 

 following end of the inner gi'eat channel, some of the more 

 marked of these dark patches appear to be associated with 

 stars to which they are adjacent. The nebula lies in the 

 neighbourhood of the Milky Way, and we should expect to 

 find as many stars projected upon it, or seen through it, as 

 are to be found in an adjacent area of equal extent, but, 

 making allowance for such stars unconnected with the 

 nebula, there seem to be stream-lines of stars which fall in 

 with the general alignement of the dark channels and the 

 great streams of nebulous matter, as well as evident groups 

 of small stars or nebulous points forming knots of nebulous 

 matter in the outer whorl of the nebula. These are better 

 seen in the original negative than on the enlargement, but 

 some of the knots of nebulous haze on the outer whorl are 

 distinctly shown on the enlargement broken up into 

 nebulous points. 



On the original negative no trace of spiral structure can 

 be seen in either of the two small nebulae, H.Y. 18 or 

 32 Messier. The nuclei of all three nebul;e appear to the 

 naked eye like stars ; but when the negative is examined 

 with a microscope, they are seen to differ in character from 

 the other star discs on the plate. They are quite black, but 

 have less definite edges than star discs of equal magnitude. 

 The appearance shown would seem to indicate that there is 

 a rapid candensation in brightness towards the centre, but 

 that the: e is no stellar nucleus. 



It shotild be mentioned that in order to facilitate com- 

 parisons with other drawings, the North point has been 

 placed uppermost upon the page. A similar remark applies 

 to the picture of the Pleiades Nebula given in the February 

 number, while telescopic views with the south point upper- 

 most have been given of the other nebulie figured in recent 

 numbers of Knowledge. A. C. R. 



