MECHANISM OF RESPIRATION 453 



muscular pressure to flow along even the finer air-passages of an 

 insect." 



As to the respiratory movements of insects, Plateau is the principal 

 authority, and the following account of the process is taken from his 

 elaborate memoir, and from the statements afterwards contributed 

 by him to Miall and Denny's "The Cockroach." 



Although many observers have superficially described the respi- 

 ratory movements of various insects, Rathke was the first one to 

 state precise views as to the mechanism of respiration. His posthu- 

 mous work, treating of the respiratory movements of the movable 

 chitinous plates of the abdomen, and of the respiratory muscles 

 characteristic of all the principal groups, filled an important blank 

 in our knowledge. But, notwithstanding the skill displayed in this 

 research, many questions still remain unanswered which require 

 more exact methods than mere observations with the naked eye or 

 the simple lens. 



Plateau, who was followed a year later by Langendorff, conceived 

 the idea of studying, by such graphic methods as are now familiar, 

 the respiratory movements of perfect insects. 



" He has made use of two modes of investigation. The first, or graphic 

 method, in the strict sense of the term, consisted in recording, upon a revolving 

 cylinder of smoked paper, the respiratory movements, transmitted by means of 

 very light levers of Bristol board attached to any part of the insect's exoskele- 

 ton. Unfortunately, this plan is only applicable to insects of more than average 

 size. A second method, that of projection, consisted in introducing the insect, 

 carried upon a small support, into a large, magic lantern fitted with a good petro- 

 leum lamp. When the amplification does not exceed 12 diameters, a sharp 

 profile may be obtained, upon which the actual displacements may be measured, 

 true to the fraction of a millimetre. Placing a sheet of white paper upon the 

 lantern screen, the outlines of the profile are carefully traced in pencil so as to 

 give two superposed figures, representing the phases of inspiration and expiration 

 respectively. By altering the position of the insect so as to obtain profiles of 

 transverse sections, or of the different parts of the body, and, further, by gluing 

 very small paper slips to parts whose movements are hard to observe, the 

 successive positions of the slips being then drawn, complete information is at 

 last obtained of every detail of the respiratory movements ; nothing is lost." 



" This method, similar to that employed by the English physiologist, Hutch- 

 inson, 1 is valuable, because it enables us, with a little practice, to investigate 

 readily the respiratory movements of very small arthropods, such as flies or 

 lady-birds. It has this advantage over all others, that it leaves no room for 

 errors of interpretation." 



" Not satisfied with mere observation by such means as these, of the respira- 

 tory movements of insects, the writer has also studied the muscles concerned, 

 and, in common with other physiologists (Faivre, Barlow, Luchsinger, Donhoff, 

 and Langendorff), has examined the action of the various nervous centres upon 



i Art, Thorax, Todd's Cycl. of Anat. aud Phys. 



