THORAX. 



1087 



to the stream is the same whether the air passes 

 into or out of the lungs, therefore the tru- 

 cheal sounds are equally heard in expiration 

 and in inspiration. But not so in the lungs ; 

 here, as the stream of air proceeds it is 

 subdivided, and with every subdivision the 

 friction is increased ; so that with every 

 advance of the stream into the substance of 

 the lung the sound is increased, and becom- 

 ing more and more buried in the substance of 

 the lung is heard as in a continual murmur. 

 In expiration the very contrary happens. 

 The friction is as quickly diminished, until 

 the substance of the lung entirely masks what 

 remains. In the larger vessels when the 

 volume of the returning air becomes great, and 

 the diameter of the tube more uniform, the 

 friction is the same whichever way the air 

 passes, and here tracheal and bronchial ex- 

 piration are audible, during inspiration as 

 well as expiration. If we take a sheep's 

 lung and inflate it, we hear the inspiratory 

 murmur; let go the air and we do not hear 

 it ; but contract part of the lung, say with the 

 edge of a paper knife, and you hear the mur- 



mur during the lung's collapsing, showing that 

 by increasing the friction you produce the 

 expiratory murmur. 



When any disease thickens or diminishes 

 the diameter of the air tubes, or when one 

 part of the lung is obliterated and another 

 part has to do double work, then the friction 

 is increased, and thus expiratory murmur is a 

 true sign of some change in the minute air 

 tubes of the lungs. Sometimes the breathing 

 murmur is so gentle and the thickness of the 

 muscles so great that we have even in health 

 known the inspiratory murmur quite inaudible. 



In organic change of the lung these sounds 

 become changed in their intensity, rhythm, and 

 character. The cause of the change of sound 

 is yet involved in much obscurity ; hence some 

 persons have been said to have had tubercular 

 lungs, when such has not been the case ; or even 

 extensive cavities, &c., yet^time has shown that 

 there never had been cavities. All the morbid 

 true sounds yet require to be verified as to their 

 cause. As we have natural changes in the 

 character of breathing, so are there changes in 

 the sounds of breathing, as follows : 



I. IN ITS INTENSITY 



II. IN ITS RHYTHM 



III. IN ITS CHARACTER 



1. Frequency 



2. Duration 



When there is fluid or disorganisation in the 

 substance of the lung, there are certain crack- 

 lings, crepitations, and gurglings, causing 

 certain other sounds not included in the above 

 list. Unfortunately authors differ in the ap- 

 plication of the names for these sounds. 

 They may be all classed under two heads, 

 the dry and the moist, whether the tubes 

 be large or small in which the sounds are pro- 

 duced. 



For the BIBLIOGRAPHY see that of art. 

 " RESPIRATION," p. 366. 



(<7. Hutchinson?) 



THYMUS GLAND. (French, Z> thymus; 

 Italian, Tiitio; German, Die Brustdruse ; Lat., 

 Thymus; Greek, 6u/toc. ) It is proposed in 

 this article to adopt the following arrange- 

 ment : First, to treat of the gland as it exists 

 in the human subject, comprehending its ordi- 

 nary and structural anatomy, and its develop- 

 ment. Secondly, to give a sketch of the 

 comparative anatomical history of the organ. 

 Thirdly, to treat of its physiology. Fourthly, 

 to mention what has been observed of morbid 

 changes occurring in it. 



HUMAN ANATOMY. Sir A. Cooper's de- 

 scription of the gland in the human subject is as 



Strong or exaggerated. 

 Feeble. 



Absent or suppressed. 

 Quick. 

 Slow. 



Jerking or interrupted. 

 Long. 

 Short. 



Expiration prolonged. 

 Harsh. 



Bronchial or tubular. 

 Cavernous. 

 . Amphoric. 



follows: "This gland is formed of a tho- 

 racic and cervical portion on each side. The 

 former is situated in the anterior mediastinum, 

 and the latter is placed in the neck, just above 

 the first bone of the sternum, and behind the 

 sterno-hyoidei and sterno-thyroidei muscles." 

 " .Between two and three months of foetal life, 

 as will be seen in the plate (fig. 717.), it is so 



Fig. 717. 



The thymus, heart, larynx, 8fc., of the human fxtus at 

 rather more than two months. (After Sir A. Cooper.) 



small as to be but just perceptible. At three 

 months (Jig. 718.) its increase is in propor- 

 tion to the relative magnitude of the foetus, and 

 thus it continues to grow gradually and equally 

 (jig. 719.) to the seventh month, when it en- 

 larges out of proportion to its former growth. 

 At eight months it is large, but at the ninth 



