LSAT 102 – Section 2 – Question 06

LSAT 102 - Section 2 - Question 06

June 1998

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT102 S2 Q06
+LR
Necessary assumption +NA
Conditional Reasoning +CondR
Causal Reasoning +CausR
A
5%
164
B
5%
160
C
84%
166
D
2%
160
E
3%
165
120
133
153
 +Easiest 148.204 +SubsectionMedium

J.Y.’s explanation

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One test to determine whether a person has been infected with tuberculosis consists of injecting the person with proteins extracted from the tuberculosis bacterium. Once a person has been infected by a bacterium, the person’s immune system subsequently recognizes certain proteins present in that bacterium and attacks the bacterium. This recognition also takes place in the test and results in a skin irritation at the injection site. Hence the physicians who designed the test reasoned that anyone who reacts in this manner to an injection with the tuberculosis proteins has been infected with tuberculosis.

Summary
The physicians conclude that anyone whose skin becomes irritated when injected with tuberculosis proteins has had tuberculosis. This is because people’s immune systems recognize proteins from bacteria that previously infected them. Furthermore, this immune system reaction also occurs (and leads to skin irritation) when someone has had tuberculosis and is then injected with tuberculosis proteins.

Notable Assumptions
The premises establish tuberculosis infection as a sufficient condition for skin irritation from this test, but not a necessary condition. However, the conclusion treats infection as being necessary. This means the physicians are assuming that there is no other reason someone’s skin would become irritated when injected with tuberculosis proteins, other than having had tuberculosis.

A
All of the proteins present in disease-causing bacteria can be recognized by the body’s immune system.
The argument is only concerned with the proteins in tuberculosis bacteria, so this kind of claim about all proteins in all disease-causing bacteria is too broad to be necessary.
B
Localized skin irritations are a characteristic symptom of tuberculosis in most people.
Whether or not skin irritation is usually a symptom of actual tuberculosis infection is irrelevant, because the argument is only concerned with reactions to the tuberculosis test.
C
The ability of the proteins present in the tuberculosis bacterium to trigger the skin irritation is exclusive to that bacterium.
In other words, there is no other bacterium which would lead to skin irritation when someone is injected with tuberculosis proteins. This is necessary because otherwise, we couldn’t conclude that a reaction meant tuberculosis and not some other bacterium.
D
Some people who have been injected with proteins extracted from the tuberculosis bacterium will contract tuberculosis as a result of the injection.
Whether or not it’s possible to get tuberculosis from being injected with tuberculosis proteins is irrelevant to whether a skin reaction truly indicates tuberculosis.
E
The body’s immune system cannot recognize infectious bacteria unless there are sufficient quantities of the bacteria to cause overt symptoms of disease.
What exactly it means to be “infected” by bacteria such that your immune system will recognize those bacteria isn’t relevant, because the argument doesn’t depend on that exact of a definition of “infected.”

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Section 1 - Reading Comprehension

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

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