April 13, 1888.] 



SCIENTIFIC NEWS. 



345 



ECONOMICAL SPHYGMOGRAPHS. 



IN order to make the beats of the pulse or of the heart 

 manifest to the eye, an apparatus is used named a 

 sphygmograph. Of this instrument there are several 

 modifications. Some, like that of Dr. Marey, are self- 

 registering and consequently high-priced. For some 

 time we have observed, says La Nature, a small apparatus 

 at the exceedingly modest price of aid., which in 

 most cases gives very satisfactory indications. It is 

 formed of a slender brass wire bent back for part of its 

 length and coiled in a spiral, the last coil being soldered 

 to a small metal cup. The other portion, which is left 

 straight, bears a little flag at its summit. 



To make use ol this instrument, it is placed 

 over the artery whose beats are to be shown, when 

 the wire supporting the flag begins to oscillate in a very 



perceptible manner. The amplitude and the frequency of 

 the oscillations vary, of course, with the persons 

 submitted to observation. 



If it be required to show the pulsations to a numerous 

 audience, it is necessary, in order to increase them suffi- 

 ciently, to have a long, light, oscillating rod, a condition 

 not easily fulfilled in practice. M. Arthur Good substi- 

 tutes, therefore, for a rod a pencil of light, which traces 

 the movements of the pulse on the wall or the ceiling of 

 a dark room, as in the accompanying figure. This pencil of 

 light may be admitted through a hole in the shutters, or 

 it may be obtained from an artificial source. In either 

 case it is directed upon a small mirror fixed in a 

 bracelet of caoutchouc, when a reflected image is thrown 

 upon the ceiling. Owing to the imperceptible move- 

 ments which the pulse impresses upon the mirror, we 

 may follow the oscillations of the reflected ray as easily 

 as those of a rigid rod, and we see the image on the 

 ceiling changing its place with more or less rapidity 



according to the rate of the pulse in the person under 

 observation. In hospitals an analogous method is 

 sometimes used to render the pulsations visible, a small 

 slip of paper being pasted over the artery to be studied. 

 The apparatus first described is entirely of metal, and 

 with it it is easy to render the movements of the artery 

 audible. It is merely necessary to solder a copper wire 

 to the cap which supports the spiral, and then to connect 

 this wire to one of the poles of a Leclanche cell. 

 The other pole of this element is connected by a second 

 wire to a small brass rod fixed by a bracelet upon the 

 arm of the patient, so that at each oscillation the rod 

 which carries the flag may impinge upon it. If a tele- 

 phone is introduced into the circuit thus formed, a click 

 is heard in the instrument at each pulsation. 



NEW METHOD OF COUNTING AIR- 

 GERMS. 



IN a previous number (p. 304) we gave an outline sketch 

 of the methods adopted by Pasteur, Tyndall, Miquel, 

 Koch, and Hesse, for ascertaining the number of micro- 

 oganisms in a definite quantity of air. Dr. P. F. Frank- 

 land has contributed a very able paper to the Royal 

 Society, in which he describes a new method of deter- 

 mining these microbes. The tubes through which the 

 air under examination is aspirated are about 5 inches in 

 length, and \ inch internal diameter. One end is slightly 

 constricted, and a plug of cotton wool, loosely packed, is 

 forced down to the constricted part from the other end of 

 the tube. About an inch from the constricted end the 

 tube is again constricted, so as to support a plug of fine 

 sugar or glass powder (passed through sieve of 40 meshes 

 to the linear inch), which has been pushed in from the 

 open end of the tube. This plug is supported in front 

 and behind by a layer of glass-wool, either plain or 

 coated with sugar. About an inch from the open end, 

 the tube is agam constricted to form a support for the 

 important plug which has to catch the germs as they 

 are being drawn in with the aspirated air. This plug is 

 constructed of a small quantity either of ordinary glass- 

 wool or of glass-wool which has been previously coated 

 with cane-sugar, by soaking it in a saturated solution of 

 the latter and then drying. Each of these plugs is about 

 the size of a pea, and with a little practice the packing 

 can be easily arranged to give the necessary degree of 

 imperviousness. The last plug — the one nearest the 

 open end of the tube — is invariably made more pervious 

 than the middle one, so that any organisms which may 

 be carried by the current of air through it may find a 

 greater resistance in the second. If the second plug is 

 afterwards found to be altogether free from organisms, it 

 clearly shows that they must have all been arrested by 

 the first plug. 



The tubes thus fitted are sterilised by being heated on 

 three successive days, for several hours each day, to a 

 temperature of 230° Fahr. in the case of those contain- 

 ing sugar, and to 320° Fahr. in the case of those which 

 only contain glass plugs. A number of tubes may be 

 conveniently sterihsed at one time in a tin box. In this 

 way several tubes can be carried about without fear of 

 contamination to the place where the experiment is to be 

 performed. 



The sterilised tube is at the place of observation 

 carefully taken from the box, and is handled by the 



