258 



SCIENCE. 



[Vol. XIX. No. 483 



SCIENCE: 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES. 



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 Fork. 



AN INSTEUMENT FOR MAPPING HOT AND COLD 



SPOTS ON THE SKIN. 



Preliminary Note. 



Various defects and incouveniences in the apparatus em- 

 ployed by Blix, Goldscheider and Donaldson led to the deter- 

 mination to produce an instrument that would present a 

 metal point of any desired temperature at any poiat of the 

 skin. The temperature must be accurately known and must 

 not vary. A registering apparatus was also to be provided, 

 and the old system of testing till a spot was found and then 

 marking it with ink was to be done away with. 



In the present instrument the hot or cold stimulus is 

 applied by water running through a small copper box that 

 comes to a point at one end. The constant stream of water 

 keeps the point at the temperature desired, and a thermometer 

 projecting from the top of the box indicates this temperature. 

 To prevent sudden changes resulting from the application to 

 the skin, the sides of the box are rather thick, thus providing 

 a mass of copper of great conductivity; a change of tempera- 

 ture at any one point is at once compensated by conduction 

 without any measurable effect on that of the whole box. 



To apply this box to the skin, an arm has been constructed 

 which can be placed in any position and which by means of 

 rack and pinion gives a motion to the box in the three planes 

 of space. The arm is supported by a ball-joint so arranged 

 that it can be clamped anywhere to a table or a chair in a 

 manner that will bring the point of the litttle box near the 

 skin-surface to be examined. Finer adjustments are made 

 by the screws of the rack and pinion. The point is now ap- 

 plied to the skin, and is moved forward by one of the screws 

 for a short distance, e.g., one centimeter, the person noticing 

 the temperature spots as the point passes over them. Then 

 the point is moved sideways one millimeter, and drawn back 

 again. In this way the whole surface can be gone over with 

 the greatest accuracy. 



On the part of the arm moving with the point is a small 

 electro-magnet carrying a pencil which descends when the 

 circuit is completed. On the part that does not move with 

 the point is a litttle flat plate, on which a piece of millimeter 

 paper is fastened. The circuit is closed by a key in the hand 

 of the person experimented upon whenever he feels a hot 

 spot or a cold spot, as the case may be. Since the pencil 

 executes the same motion as the point the result is an accurate 

 map of the spots directly on the millimeter paper, 



E. W. Scripture, Ph.D. (Leipzig). 



Clark University, Worcester, Mass. ' 



SOME USES OF BACTERIA.' 



Every farmer, of course, ajipreciates the value of keeping stock, 

 and you all know that you cannot run a farm without your cows, 

 your horses, your sheep, your hens, and your pigs. You do not 

 appreciate, however, that it is just as necessary to keep a stock 

 of bacteria on hand, on your farm, to carry on your farming opera- 

 tions. The farmer has learned to-day that he must keep a good 

 breed of cows and a good breed of stock in general, but farmers- 

 generally do not appreciate that it is equally necessary to keep a 

 good breed of bacteria. You cannot make butter or cheese with- 

 out cows ; you cannot make butter or cheese satisfactorily without 

 bacteria. You cannot cultivate your fields without your horses to 

 help you, but all the cultivation that you might give your fields 

 would be useless were it not that these little creatures of which I 

 shall speak this morning come in after you get through and com- 

 plete the process which you have begun. 



Now, probably many of you have never particularly thought 

 that your farm is stocked with bacteria, but they are there. They 

 are in your brooks, in your springs, in your wells, in your rivers;^ 

 they are in your dairy, in your milk, in your butter, in your cheese, 

 in your barn. They are in the air, they are in the soil, and your 

 manure heap is a paradise for them. 



Bacteria are in rather bad odor in the minds of most people,, 

 and we are all inclined to look with hon-or upon them. We have 

 a sort of shrinking when any one speaks to us of the number of 

 bacteria in the milk which we drink. The reason for this, how- 

 ever, is simply an historical one. When bacteria were first dis- 

 covered it was early noticed that they had a causal relation to dis- 

 ease, and scientists went to work from the very first to investigate 

 diseases in relation to bacteria. The result was that after a few 

 years a great deal of information had accumulated showing that 

 bacteria caused diseases. The so-called " epidemics " are usually 

 the result of bacteria, and with minds intent upon this side of the 

 question scientists did not pay much attention to the good that 

 bacteria might do in the world. It was more interesting to study 

 disease. People are very much interested when you begin to telL 

 them why it is that they have small-pos, why it is that they have 

 yellow-fever; the other side of the matter, however, is not sO' 

 interesting. 



But the fact is that the bacteria story has only been half told, 

 and thus far it is the smaller half that has been told, if there is- 

 such a thing as the smaller half. It is true that bacteria are occa- 

 sionally injurious to us, but it is equally true that they are of 

 direct benefit to us. Hitherto we have looked upon bacteria as 

 belonging to the medical profession; we think the doctors ought 

 to know about them because they produce disease, but ordinary 

 people do not need to bother themselves with these things. Biit I 

 think, before I get through with my talk this morning, you wiU 

 see that bacteria have a very much closer relation to you as- 

 farmers than they do to the doctors. It is the farmer to-day who- 

 ought to understand bacteriology. It is well enough for the medi- 

 cal man to understand the subject also, but bacteriology has 

 already become a medical subject, while the agriculturist has- 

 generally neglected it. 



I propose in my talk this morning to point out to you a few 

 of the benefits which you as farmers derive from the agency of 

 these microscopic organisms. I shall divide the subject into four 



1 -\n address by Dr. H. W. Conn, Wesleyan University, Middletown, Conn- 



