232 
‘vouring grasses of different kinds, to purge 
off the sordes. In cold, wet weather, the 
animal is frequently affected with colic, 
which it endeavours to remove in this 
way. Of this, I have often been an cye- 
witness, at a time when I kuew not the 
cause, but wondered to see dogs tear up 
and eat grass with the avidity of a cow or 
ahorse. In the good effects of purga- 
tives carly administered to dogs, when in- 
disposed, ‘Lhave a firm belief; and doubt 
not but the experience of many of my 
readers enables them to say as much. 
I might adauce some exainples, had 
not my present letter stretched out alrea- 
dy totoogreatalength. ‘This, theretore, 
with some further arguments to show 
that rabies is preduced spontaneously, 
and primarily in the animal itself, as well 
as by inoculation, I shail reserve ull my 
next communication, in which [ hope sa- 
tistactorily to prove what I have under- 
taken on this head to assert. 
Yow’s, &c. RK. Hamiton, 
—— 
To the Editor of the Monthly Magazine. 
SIR, 
O writer on vegetable physiology, so 
¥ far as I know, has hitherto noticed 
the high degree of irritability displayed by 
the garden lettuce, /ucfuca sativa, at cer- 
ain periods of its grewth. Some account 
therefore of the recent experiments made 
on this interesting plant by Dr. J. Carra- 
dorri, a distinguished naturalist, must, I 
conceive, prove higlily acceptable to the 
lovers of phytological science. 
From his experiments, it would appear, 
that if a lettuce plant be gently touched 
with the finger, when it is in seed, and 
particularly when in flower, it may be 
observed to emit, at the place so touched, 
a milky liquor, in the form of very ini- 
nute drops. This phenomenon occurs 
- however only in the small amplexicaul 
leaves of the branches, 
_ the calyxes or flower-cups. The contact 
of any solid body, however smooth; even 
the application of the slightest stimulus 
operates to produce the emission of this 
liquor. A blade of grass, Or airy other 
pointed body, applied i ir the most gentie 
manner, excites in the part such a degree 
of irritation as to make it throw out a 
milky hamour in the form of jets, which 
an attentive eye may readily perceive 
spurting into the air to some distance. 
Neither a drop cf water, nor of the 
nitrous, sulpbureous, wer muriatic acids, 
when applied very gently, so as to pro- 
duce no mechanical impulse, appeared to 
3 
and the Jeafiets of 
Dr. Carradorri’s Experiments on the Irritability (Oct. 1, 
Carradorri capable of exciting thé 
ae emission from the most irritable 
parts of the plant; bat when one ormore 
drops of any fuid were made to fall upon 
it, they never failed to produce an emis- 
sion of the milky juice. 
Neither the smoke of tobacco, nor the 
fumes of the nitric and sulphuric acids, 
produced the least effect. Dr. Carra- 
dorri next directed upon it a stream of 
air, by blowing through a straw with all 
his force; but, unless when he approach- 
ed extremely near, not the smallest effect 
was produced. 
The application of heat by means of a 
burning coal, or red-hot iron, appeared to 
have no other influence, but that. of de- 
stroying the portion of the plant near to 
which they were brought; néither did the 
action of cold, nor the application of ice, — 
produce in this vegetable any sensible 
change. But the slightest touch of an in- 
sect was suficient to excite the irritability 
of the plan, and produce an emission of 
the milky liquor. It is OTe inter= 
esting to observe, says Carradorri, 
how the ants, which etude creep 
upon this plant, i in order to collect, and 
carry off its seeds, are entangled in the 
milky juice exuding from it, in conse- 
quence of the slight impression made by 
their feet. Sucha sight, ke adds, recall- 
ed to my mind the fabulous representa- 
tion of the rivulets of milk, described by 
the poets as having their source in Ely- 
a , abounding with delicacies of every: 
ind— 
Flumina jam lactis, jam flumina nectaris ibant. 
These plants, torn up by the roots, or 
their branches detached from the stem or 
trunk, furnish, on the application of sti- 
muil, the same exudation, in whatever 
place they nay be kept, so long as they 
possess a certain degree of vitality, or 
vegetative power, - 
Having tern up a lettuce when in full 
flower, a und possessing the most certain 
signs of irritability, Dr. Carradorri im- 
mersed it slowly, while holding it in an 
uprieht position, in a vessel of water; 
as the water came into contact with the 
leaves of the plant, or the leaflets of the 
calyx, it excited them to eject the milky 
liquor with which they were furnished. — 
On applying stimuli to the plant when ~ 
tinder water, a similar emission of juice 
took place, as when it was excited in the 
air; and when the excitement was some=-_ 
whit greater, he could discern the milky 
liquor thrown by jets into the water. 
This unquestionably must have proceeded, 
ini 
<S 
